bug#9983: valgrind warning in draw_glyphs

[Eli Zaretskii <eliz@gnu.org>]

> From: Dan Nicolaescu <dann@gnu.org>
> Date: Sun, 06 Nov 2011 23:36:42 -0500
> 
> The warning is for this:
>         if (check_mouse_face
>               && mouse_beg_col < start && mouse_end_col > i)
> 
> it looks like mouse_beg_col and mouse_end_col could be left uninitialized a few lines above.

I don't see how.  These variables are initialized in this block:

	  if (row >= mouse_beg_row && row <= mouse_end_row)
	    {
	      check_mouse_face = 1;
	      mouse_beg_col = (row == mouse_beg_row)
		? hlinfo->mouse_face_beg_col : 0;
	      mouse_end_col = (row == mouse_end_row)
		? hlinfo->mouse_face_end_col
		: row->used[TEXT_AREA];
	    }

check_mouse_face starts as zero, and is only set to 1 in this block.
So any test that is conditioned on check_mouse_face being non-zero is
okay with looking at mouse_beg_col and mouse_end_col.

The other variables in the line being flagged, `start' and `i', are
also okay: `start' is one of the call arguments and `i' is computed
right before the line being flagged.

Did I miss something?