windows: Call GetWindowText() with the correct parameters (thanks, Zebediah!)

GetWindowText() wants you to tell it the size of the buffer--including the
terminating NULL char--but we weren't counting that last char, losing the
last char of the string in the process. This was only seen with the special
case of SDL_CreateWindowFrom() to use an existing native window, not
the usual SDL_CreateWindow() codepath.

Fixes Bugzilla #4696.
1 file changed