shared/cairo-util: Release any fontmap laying around

This is particularly useful when using the weston-editor which seems to
cause an issue with cairo_debug_reset_static_data(), as that still seems
to find out there are references laying around, causing a crash when
exiting:

 ../../../../src/cairo-hash.c:217: _cairo_hash_table_destroy: Assertion
 `hash_table->live_entries == 0' failed

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

shared/cairo-util.c

@@ -691,6 +691,10 @@ theme_get_location(struct theme *t, int x, int y,
 void
 cleanup_after_cairo(void)
 {
+	/* some clients, particular weston-editor, still creates indirectly a
+	 * new font map; this makes sure we untie that up and avoid an assert
+	 * from cairo */
+	pango_cairo_font_map_set_default(NULL);
 	cairo_debug_reset_static_data();
 #ifdef HAVE_PANGO
 	FcFini();