libgimp, plug-ins: Prevent GFig crash with NULL brush

The GFig plug-in assumes that there is always
a valid brush selected when creating its
dialogue. However, a NULL brush is possible,
and GFig's assumption can cause a crash
in GIMP by attempting to get a buffer from
a NULL brush.
This patch adds conditional checks for the
brush to not be NULL before using it.

app/pdb/brush-cmds.c

@@ -162,19 +162,22 @@ brush_get_info_invoker (GimpProcedure         *procedure,
     {
       GimpTempBuf *mask   = gimp_brush_get_mask (brush);
       GimpTempBuf *pixmap = gimp_brush_get_pixmap (brush);
-      const Babl  *format;
+      const Babl  *format = NULL;
 
-      format = gimp_babl_compat_u8_mask_format (
+      if (brush)
-        gimp_temp_buf_get_format (mask));
+        format = gimp_babl_compat_u8_mask_format (gimp_temp_buf_get_format (mask));
 
       width    = gimp_brush_get_width  (brush);
       height   = gimp_brush_get_height (brush);
-      mask_bpp = babl_format_get_bytes_per_pixel (format);
 
-      if (pixmap)
+      if (format)
+        mask_bpp = babl_format_get_bytes_per_pixel (format);
+      else
+        mask_bpp = 0;
+
+      if (pixmap && format)
         {
-          format = gimp_babl_compat_u8_format (
+          format = gimp_babl_compat_u8_format (gimp_temp_buf_get_format (pixmap));
-            gimp_temp_buf_get_format (pixmap));
 
           color_bpp = babl_format_get_bytes_per_pixel (format);
         }

libgimp/gimpbrushchooser.c

@@ -217,6 +217,8 @@ gimp_brush_chooser_get_brush_bitmap (GimpBrushChooser *chooser,
   GimpBrush *brush;
 
   g_object_get (chooser, "resource", &brush, NULL);
+  if (! brush)
+    return;
 
   if (chooser->brush  == brush &&
       chooser->width  == width &&

pdb/groups/brush.pdb

@@ -138,19 +138,22 @@ HELP
 {
   GimpTempBuf *mask   = gimp_brush_get_mask (brush);
   GimpTempBuf *pixmap = gimp_brush_get_pixmap (brush);
-  const Babl  *format;
+  const Babl  *format = NULL;
 
-  format = gimp_babl_compat_u8_mask_format (
+  if (brush)
-    gimp_temp_buf_get_format (mask));
+    format = gimp_babl_compat_u8_mask_format (gimp_temp_buf_get_format (mask));
 
   width    = gimp_brush_get_width  (brush);
   height   = gimp_brush_get_height (brush);
-  mask_bpp = babl_format_get_bytes_per_pixel (format);
 
-  if (pixmap)
+  if (format)
+    mask_bpp = babl_format_get_bytes_per_pixel (format);
+  else
+    mask_bpp = 0;
+
+  if (pixmap && format)
     {
-      format = gimp_babl_compat_u8_format (
+      format = gimp_babl_compat_u8_format (gimp_temp_buf_get_format (pixmap));
-        gimp_temp_buf_get_format (pixmap));
 
       color_bpp = babl_format_get_bytes_per_pixel (format);
     }

plug-ins/gfig/gfig-dialog.c

@@ -630,6 +630,7 @@ gfig_dialog (GimpGfig *gfig)
   gfig_list_load_all (gfig_path);
 
   /* Setup initial brush settings */
+  if (gimp_context_get_brush ())
     set_context_bdesc (gimp_context_get_brush ());
 
   gtk_widget_show (main_hbox);

plug-ins/gfig/gfig-style.c

@@ -533,6 +533,7 @@ gfig_brush_changed_callback (gpointer               user_data,
   current_style->brush = brush;
 
   /* this will soon be unneeded. How soon? */
+  if (brush)
     set_context_bdesc (brush);
 
   gimp_context_set_brush (brush);
@@ -660,6 +661,8 @@ gfig_read_gimp_style (Style       *style,
   style->fill_opacity = 100.;
 
   /* Cache attributes of brush. */
+  if (style->brush)
+    {
       gimp_brush_get_info (style->brush,
                            &style->brush_width, &style->brush_height,
                            &dummy, &dummy);
@@ -667,6 +670,16 @@ gfig_read_gimp_style (Style       *style,
 
       set_context_bdesc (style->brush);
     }
+  else
+    {
+      style->brush_width   = 1;
+      style->brush_height  = 1;
+      style->brush_spacing = 1;
+
+      gfig_context->bdesc.width  = 48;
+      gfig_context->bdesc.height = 48;
+    }
+}
 
 /*
  * gfig_style_set_content_from_style() sets all of the style control widgets
@@ -695,15 +708,19 @@ gfig_style_set_context_from_style (Style *style)
 
   gimp_context_set_brush_default_size ();
 
+  if (style->brush)
     gimp_resource_chooser_set_resource (GIMP_RESOURCE_CHOOSER (gfig_context->brush_select),
                                         GIMP_RESOURCE (style->brush));
 
+  if (style->pattern)
     gimp_resource_chooser_set_resource (GIMP_RESOURCE_CHOOSER (gfig_context->pattern_select),
                                         GIMP_RESOURCE (style->pattern));
 
+  if (style->gradient)
     gimp_resource_chooser_set_resource (GIMP_RESOURCE_CHOOSER (gfig_context->gradient_select),
                                         GIMP_RESOURCE (style->gradient));
 
+  if (style->brush)
     set_context_bdesc (style->brush);
 
   if (gfig_context->debug_styles)