Avoid flashing the console window on startup

Also, center on the primary screen only by default (some would say the active screen is better, I'm not sure how to detect that...)  Fixes #4207, which was mostly just my todo item.

Anyway, this just doesn't even open the console until it's shown.  It's already buffering the output for the thread, so you'll still get log data even if you don't open it immediately.

The only possible problem is if it overflows the buffer, which is more likely now (since nothing's reading it.)  But, I'm sure I tested that before, so it should be fine, I think... it could be slightly slower (when logging), though, if it hits the buffer size.  I don't think it's a big deal.

Also added two smaller fixes, one unrelated (crash in debugger), and the other also ui related - drag and drop was hanging when no game was loaded yet.

-[Unknown]