Unexpected behavior when az FM rate correction can not be computed:

[hfattahi]

Checked for duplicates

Yes - I've already checked

Describe the bug

Currently if the user asks to compute Az FM rate correction, but the computation is not possible because of lack of metadata, then the function here and here silently goes on and returns a zero LUT instead of simply throwing an exception and failing the process.

What did you expect?

If the user asks for computing AZ FM rate correction and the computation not possible because of lack of metadata I expected the reader to throw an exception and exit. The reason is that if we have two SLCs and we successfully and correctly compute the Az FM rate for one and fail to compute Az FM rate for the other but rather return ZERO LUT then we will end up with one coregistered SLC which has accounted for Az FM rate mismatch and the other which has not and therefore we would end up with significant interferometric burst discontinuities in results of artificial offsets introduced by correcting az FM rate for one SLC and not correcting for the other.

Reproducible steps

No response

Environment

No response