Avoid assertion violations in --enable-checking builds

* src/xdisp.c (gui_produce_glyphs): Make sure character glyphs
don't trigger assertion violation due to negative ascent or
descent.  This was reporte dto happen with some fonts used by the
xfont backend.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 24049ab4e33..9f93799783d 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -31199,6 +31199,11 @@ gui_produce_glyphs (struct it *it)
           it->max_ascent = max (it->max_ascent, font_ascent);
           it->max_descent = max (it->max_descent, font_descent);
         }
+
+      if (it->ascent < 0)
+        it->ascent = 0;
+      if (it->descent < 0)
+        it->descent = 0;
     }
   else if (it->what == IT_COMPOSITION && it->cmp_it.ch < 0)
     {