Work around cairo limitations

If we just draw an image, cairos recording surface
complains that it is unbounded. Its not true of course.

To make things work, clip to the extents.

src/hb-ot-color-cbdt-table.hh

@@ -956,6 +956,11 @@ struct CBDT
       if (unlikely (!get_extents (font, glyph, &pixel_extents, false)))
         return false;
 
+      funcs->push_clip_rectangle (data,
+                                  extents.x_bearing, extents.y_bearing,
+                                  extents.x_bearing + extents.width,
+                                  extents.y_bearing + extents.height);
+
       funcs->image (data,
 		    blob,
 		    pixel_extents.width, -pixel_extents.height,
@@ -963,6 +968,8 @@ struct CBDT
 		    font->slant_xy,
 		    &extents);
 
+      funcs->pop_clip (data);
+
       hb_blob_destroy (blob);
       return true;
     }

util/hb-cairo-utils.c

@@ -180,6 +180,15 @@ hb_cairo_paint_glyph_image (cairo_t *cr,
   if (!surface)
     return;
 
+  cairo_save (cr);
+  /* this clip is here to work around recording surface limitations */
+  cairo_rectangle (cr,
+                   extents->x_bearing,
+                   extents->y_bearing,
+                   extents->width,
+                   extents->height);
+  cairo_clip (cr);
+
   cairo_pattern_t *pattern = cairo_pattern_create_for_surface (surface);
   cairo_pattern_set_extend (pattern, CAIRO_EXTEND_PAD);
 
@@ -200,6 +209,8 @@ hb_cairo_paint_glyph_image (cairo_t *cr,
 
   cairo_pattern_destroy (pattern);
   cairo_surface_destroy (surface);
+
+  cairo_restore (cr);
 }
 
 static void