MFDv5: allow user input even if noiseSFTs already have window info, only fail if inconsistent?

Hi @karl-wette in trying to adapt PyFstat to the new SFT convention, I noticed that it seems quite complicated to write wrapper code that deals flexibly with noiseSFTs and windows: it looks like one currently would always need to know beforehand, or check with a try-except, whether the given SFTs have the window header info, and correspondingly pass the info or not.

What would it make much simpler would be to change the strict error in these lines to one that gets thrown only if they're inconsistent. If you have no objections, I can make a quick MR with a check like this: XLAL_CHECK ( ( strcmp( window_type_from_noiseSFTs, window_type_from_uvar ) == 0 ) && ( window_param_from_noiseSFTs == window_param_from_uvar ), XLAL_EINVAL, "Inconsistent SFT window between --noiseSFTs and user input: [%s,%f] vs [%s,%f].", window_type_from_noiseSFTs, window_param_from_noiseSFTs, window_type_from_uvar, window_param_from_uvar );

But I wanted to check first if you had good reasons to explicitly forbid this, maybe worrying about precision issues when checking the REAL8 window_param?