Importing a reactor with instance in a mode triggers a NPE

[edwardalee]

File lib/InstanceInMode.lf instantiates a reactor inside a mode:

target C
reactor U {
  reaction(startup) {==}
}
reactor B {
  reaction(startup) {==}
  initial mode A {
    u = new U()   
  }
}

File ImportInstanceInMode.lf imports the outer reactor:

target C {
  timeout: 0s
}
import B from "lib/InstanceInMode.lf"
main reactor {
  b = new B()
}

Compiling this program triggers a null-pointer exception.

[edwardalee]

This is fixed in PR #2270.