Update our idea of our terminal's dimensions even outside of TUI

Update our idea of our terminal's dimensions even outside of TUI

When in the CLI, GDB's "width" and "height" variables are not kept in sync
when the underlying terminal gets resized.

This patch fixes this issue by making sure sure to update GDB's "width"
and "height" variables in the !tui_active case of our SIGWINCH handler.

gdb/ChangeLog:

	* tui/tui-win.c (tui_sigwinch_handler): Remove now-stale comment.
	(tui_sigwinch_handler): Still update our idea of
	the terminal's width and height even when TUI is not active.