save_images does not correctly check for frame availability

[Breakthrough]

When using save-images functionality via CLI or API, some videos will result in an exception being thrown with the OpenCV backend. Other backends can be used as a workaround until a fix is landed.

Discussed in #454

^{Originally posted by pengyouak October 26, 2024}

Some videos will throw this error halfway through the process

bool' object has no attribute 'shape'