Avoid assertion violations in maybe_produce_line_number

* src/xdisp.c (redisplay_window): Make sure desired_matrix is
cleared before calling try_window.  This is important when
display-line-numbers is non-nil, because line-number display code
assumes each glyph row is completely cleared when it is called to
produce a line number.  (Bug#32358)

src/xdisp.c

@@ -16897,6 +16897,7 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
       /* We used to issue a CHECK_MARGINS argument to try_window here,
 	 but this causes scrolling to fail when point begins inside
 	 the scroll margin (bug#148) -- cyd  */
+      clear_glyph_matrix (w->desired_matrix);
       if (!try_window (window, startp, 0))
 	{
 	  w->force_start = true;