* Added a new RNA subtype, PROP_IMAGEPATH. It's the same as PROP_FILEPATH, but for images only.

* Changed UI code to display image browser for PROP_IMAGEPATH
* Set the icon_filepath RNA property for brushes to use PROP_IMAGEPATH
* Changed preview icon drawing to ignore unset icons
* Fixed const warnings in brush RNA

source/blender/editors/interface/interface_widgets.c

@@ -748,6 +748,9 @@ static void widget_draw_preview(BIFIconID icon, float aspect, float alpha, rcti
 {
 	int w, h, x, y, size;
 
+	if(!icon)
+		return;
+
 	w = rect->xmax - rect->xmin;
 	h = rect->ymax - rect->ymin;
 	size = MIN2(w, h);