Fix the AssertionError when calling masker in coco_eval.py (#213)

* fix the same issue as #185

* add fix from the previous change

maskrcnn_benchmark/data/datasets/evaluation/coco/coco_eval.py

@@ -116,7 +116,10 @@ def prepare_for_coco_segmentation(predictions, dataset):
         prediction = prediction.resize((image_width, image_height))
         masks = prediction.get_field("mask")
         # t = time.time()
-        masks = masker(masks, prediction)
+        # Masker is necessary only if masks haven't been already resized.
+        if list(masks.shape[-2:]) != [image_height, image_width]:
+            masks = masker(masks.expand(1, -1, -1, -1, -1), prediction)
+            masks = masks[0]
         # logger.info('Time mask: {}'.format(time.time() - t))
         # prediction = prediction.convert('xywh')