Fix Faster-RCNN d2_convert error. (#1389)

examples/FasterRCNN/convert_d2/convert_d2.py

@@ -109,6 +109,7 @@ def convert_weights(d, cfg):
         _convert_box_predictor("roi_heads.box_predictor", "fastrcnn/outputs" if has_fpn else "fastrcnn")
 
     # mask head
+    if cfg.MODEL.MASK_ON:
         for fcn in range(cfg.MODEL.ROI_MASK_HEAD.NUM_CONV):
             _convert_conv(f"roi_heads.mask_head.mask_fcn{fcn+1}", f"maskrcnn/fcn{fcn}")
         _convert_conv("roi_heads.mask_head.deconv", "maskrcnn/deconv")