Fix bug #11813 with invalid font for buffer name on the modeline.

 src/xdisp.c (fill_glyphless_glyph_string): If the face of the glyph
 has no font, use the frame's font.

src/ChangeLog

+2012-07-08  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (fill_glyphless_glyph_string): If the face of the glyph
+	has no font, use the frame's font.  (Bug#11813)
+
 2012-07-07  Andreas Schwab  <schwab@linux-m68k.org>
 	* xdisp.c (display_line): Avoid warning about implicit declaration

src/xdisp.c

@@ -22736,7 +22736,7 @@ fill_glyphless_glyph_string (struct glyph_string *s, int face_id,
   last = s->row->glyphs[s->area] + end;
   voffset = glyph->voffset;
   s->face = FACE_FROM_ID (s->f, face_id);
-  s->font = s->face->font;
+  s->font = s->face->font ? s->face->font : FRAME_FONT (s->f);
   s->nchars = 1;
   s->width = glyph->pixel_width;
   glyph++;