Clearer Error Message for Transaction Not Found

[leofofeo]

Is your feature request related to a problem? Please describe.
Sending a message to an address with no transactions results in a long error of type "Transaction not found"

Describe the solution you'd like
Map error to a clearer and more concise description of the error.

Additional context

status 500: No transactions found for `address`
github.com/mailchain/mailchain/internal/clients/etherscan.getFromResultHash
	/go/src/github.com/mailchain/mailchain/internal/clients/etherscan/pubkey-finder.go:63
github.com/mailchain/mailchain/internal/clients/etherscan.APIClient.PublicKeyFromAddress
	/go/src/github.com/mailchain/mailchain/internal/clients/etherscan/pubkey-finder.go:37
github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers.GetPublicKey.func1
	/go/src/github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers/pubkey.go:56
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:1995
github.com/gorilla/mux.(*Router).ServeHTTP
	/go/pkg/mod/github.com/gorilla/[email protected]/mux.go:212
github.com/urfave/negroni.Wrap.func1
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:46
github.com/urfave/negroni.HandlerFunc.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:29
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/rs/cors.(*Cors).ServeHTTP
	/go/pkg/mod/github.com/rs/[email protected]/cors.go:240
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/urfave/negroni.(*Negroni).ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:96
net/http.serverHandler.ServeHTTP
	/usr/local/go/src/net/http/server.go:2774
net/http.(*conn).serve
	/usr/local/go/src/net/http/server.go:1878
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:1337
github.com/mailchain/mailchain/internal/clients/etherscan.APIClient.PublicKeyFromAddress
	/go/src/github.com/mailchain/mailchain/internal/clients/etherscan/pubkey-finder.go:39
github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers.GetPublicKey.func1
	/go/src/github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers/pubkey.go:56
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:1995
github.com/gorilla/mux.(*Router).ServeHTTP
	/go/pkg/mod/github.com/gorilla/[email protected]/mux.go:212
github.com/urfave/negroni.Wrap.func1
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:46
github.com/urfave/negroni.HandlerFunc.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:29
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/rs/cors.(*Cors).ServeHTTP
	/go/pkg/mod/github.com/rs/[email protected]/cors.go:240
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/urfave/negroni.(*Negroni).ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:96
net/http.serverHandler.ServeHTTP
	/usr/local/go/src/net/http/server.go:2774
net/http.(*conn).serve
	/usr/local/go/src/net/http/server.go:1878
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:1337
github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers.GetPublicKey.func1
	/go/src/github.com/mailchain/mailchain/cmd/mailchain/internal/http/handlers/pubkey.go:62
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:1995
github.com/gorilla/mux.(*Router).ServeHTTP
	/go/pkg/mod/github.com/gorilla/[email protected]/mux.go:212
github.com/urfave/negroni.Wrap.func1
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:46
github.com/urfave/negroni.HandlerFunc.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:29
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/rs/cors.(*Cors).ServeHTTP
	/go/pkg/mod/github.com/rs/[email protected]/cors.go:240
github.com/urfave/negroni.middleware.ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:38
github.com/urfave/negroni.(*Negroni).ServeHTTP
	/go/pkg/mod/github.com/urfave/[email protected]/negroni.go:96
net/http.serverHandler.ServeHTTP
	/usr/local/go/src/net/http/server.go:2774
net/http.(*conn).serve
	/usr/local/go/src/net/http/server.go:1878
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:1337

[stale]

This issue has been automatically marked as stale because it has not had recent activity. The resources of the Mailchain team are limited, and so we are asking for your help. If this is a bug and you can still reproduce this error on the master branch, please reply in order to keep the issue open. If this is a feature request, and you feel that it is still relevant and valuable, please reply in order to keep the issue open. This issue will automatically be closed in the near future if no further activity occurs. Thank you for all your contributions.