Update LoadStreams init fallbacks (#3295)

utils/datasets.py

@@ -284,8 +284,8 @@ class LoadStreams:  # multiple IP or RTSP cameras
             assert cap.isOpened(), f'Failed to open {s}'
             w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
             h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
-            self.fps[i] = (cap.get(cv2.CAP_PROP_FPS) % 100) or 30.0  # assume 30 FPS if cap gets 0 FPS
-            self.frames[i] = int(cap.get(cv2.CAP_PROP_FRAME_COUNT)) or float('inf')  # assume infinite stream if 0 len
+            self.fps[i] = max(cap.get(cv2.CAP_PROP_FPS) % 100, 0) or 30.0  # 30 FPS fallback
+            self.frames[i] = max(int(cap.get(cv2.CAP_PROP_FRAME_COUNT)), 0) or float('inf')  # infinite stream fallback
 
             _, self.imgs[i] = cap.read()  # guarantee first frame
             self.threads[i] = Thread(target=self.update, args=([i, cap]), daemon=True)