Deny Invalid Mex Orders gadget (cmd_mex_denier.lua) issues with inserted/prepended commands

[A-Lias]

Description

It appears that the fix to #2641 introduced a new bug that rejects a valid mex build order if the placement is exactly on the metal spot and the command is inserted at the beginning of the command queue (holding space bar, or whatever hotkey you use).

Additionally, issuing a mex build order at an invalid spot with the prepend key held down correctly snaps to the proper location, but the rest of the queued orders are removed. (This is a related, but different issue. I will open a new issue for this.)

Expected Behaviour

A command to place a mex directly on top of a metal spot should be allowed even when the build command is prepended (holding space bar).

Actual Behaviour

A prepended mex build command directly on top of a metal spot will be denied with the warning "Extractors cannot be placed off of metal spots"

Reproduction steps

To replicate: Issue a mex build order exactly on the metal spot while holding spacebar (or whatever your hotkey is for "insert command"/prepend command). The order will be denied.

Other

There seem to be a number of bugs that cause this issue:

This line

Beyond-All-Reason/luarules/gadgets/cmd_mex_denier.lua

Line 50 in c488447

bx, bx = cmdParams[4], cmdParams[6] -- this is where the cmd position is placed in prepended commands with commandinsert

seems wrong: it should be

bx, bz = cmdParams[4], cmdParams[6]

Additionally,

Beyond-All-Reason/luarules/gadgets/cmd_mex_denier.lua

Lines 40 to 42 in c488447

	if cmdID == CMD_INSERT then
	cmdID = cmdParams[2] -- this is where the ID is placed in prepended commands with commandinsert
	end

overwrites cmdID, so the check later

Beyond-All-Reason/luarules/gadgets/cmd_mex_denier.lua

Lines 49 to 51 in c488447

	if cmdID == CMD_INSERT then
	bx, bx = cmdParams[4], cmdParams[6] -- this is where the cmd position is placed in prepended commands with commandinsert
	end

will never execute.

I don't have time to test and issue a PR right now, but I think something like this should work for the main placement issue.

if cmdID == CMD_INSERT then
	adjustedCmdID = cmdParams[2] 
end

if not isMex[-adjustedCmdID] then
	return true
end

local bx, bz = cmdParams[1], cmdParams[3]
if cmdID == CMD_INSERT then
	bx, bz = cmdParams[4], cmdParams[6]
end

[A-Lias]

Fixed by #2652 and #2653 and #2671