[Fix] Adapt YOLOv5 pipeline to handle models with dynamic HxW (#967)

* initial commit

* Update src/deepsparse/yolo/pipelines.py

src/deepsparse/yolo/pipelines.py

@@ -163,6 +163,12 @@ class properties into an inference ready onnx file to be compiled by the
         model_path = model_to_path(self.model_path)
         if self._image_size is None:
             self._image_size = get_onnx_expected_image_shape(onnx.load(model_path))
+            if self._image_size == (0, 0):
+                raise ValueError(
+                    "The model does not have a static image size shape. "
+                    "Specify the expected image size by passing the"
+                    "`image_size` argument to the pipeline."
+                )
         else:
             # override model input shape to given image size
             if isinstance(self._image_size, int):

src/deepsparse/yolo/utils/utils.py

@@ -359,6 +359,8 @@ def modify_yolo_onnx_input_shape(
     model_input = model.graph.input[0]
 
     initial_x, initial_y = get_onnx_expected_image_shape(model)
+    if initial_x == initial_y == 0:
+        initial_x, initial_y = image_shape
 
     if not (isinstance(initial_x, int) and isinstance(initial_y, int)):
         return model_path, None  # model graph does not have static integer input shape