Fix middlegame mouse control and improve corresponding error messaging

[kcgen]

The middlegame mouse control was not taking effect; thanks to @arrowgent for reporting this regression.

This PR also improves the error messaging when the the mouse control settings are missing or incorrect, also suggested by @arrowgent. See commit comment for new output: 4aece2e

Will await feedback to see if this addresses the points here: 4aece2e

(Tested on Linux)

[dreamer]

Tested it and implementation is ok; it's also small and clean, so perfect :)

@kcgen Please adjust the commit messages for both commits this way:

• First commit: fix type nane -> name (also commit subject seems weird…)
• Second commit: we don't have a bug report to refer to in second commit (creating one at this point would be silly). Please explain in commit message body the effect accomplished by this change. I will definitely want to include this in release notes for 0.76.0, but hunting down what was fixed by exact commit will be pretty annoying.

After commit messages will be adjusted, I'll merge it right away.

@arrowgent Thank you for the report and pointing out the issue :) Next time don't hesitate to create a new bug report - it's easier for us in the long term.

[kcgen]

@dreamer , thanks for flagging both of these poorly worded commits. Hopefully the updates describe them clearly.

Was it too early, too late, not enough tea? I'm out of excuses -- a good reminder for myself to always make a second review pass!

[dreamer]

Found one more typo, but this time the fix was obvious ;) Merged in: 66e56da

@kcgen Thanks for clean fix! @arrowgent thank you for the report :)