tr_image: detect $name as builtin or generated image

Author: illwieckz

src/engine/renderer/tr_image.cpp

@@ -1821,7 +1821,7 @@ image_t *R_FindImageFile( const char *imageName, imageParams_t &imageParams )
 			// Built-in images can't be reloaded with different parameters, so return them as-is.
 			// For most of the usable ones e.g. _white, parameters wouldn't make a difference anyway.
 			// HACK: detect built-in images by naming convention, though nothing stops users from using such names
-			if ( image->name[ 0 ] == '_' && !strchr( image->name, '/' ) )
+			if ( ( image->name[ 0 ] == '$' || image->name[ 0 ] == '_' ) && !strchr( image->name, '/' ) )
 			{
 				return image;
 			}