Consistent IFASMFDL behaviour for empty logstreams

Currently there are two possible outcomes when using IFASMFDL and specifying a time frame where no records can be found in the logstream, depending on whether the logstream has been written to. If there are no records in the specified time frame, but there are records prior to the given start time, then IFASMFDL will write message "IFA812I IFASMFDL REQUEST INCORRECT FOR LOGSTREAM (...) POSSIBLE BAD PARAMETER-BLOCKLEN" and end with RC=4. That is very confusing, given that the issue really is as simple as that there is no record found. If there has never been written a single block to the logstream since it's creation, then IFASMFDL will exit with RC=0 and write message "IFA023I LOGSTREAM IS EMPTY". Now that is quite on point.

Please change the behaviour in the first case so that
a) a more precise message is written, like "IFA0xxI NO RECORDS IN SPECIFIED TIMEFRAME"
b) IFASMFDL ends with RC=0 indicating that there was no problem processing.

One could argue that having no records in the given time frame could indeed be a problem, so RC=0 would be incorrect. Therefore, you could introduce a keyword like "ALLOWEMPTY(TRUE)", which would result in RC=0, as I described. If the keyword is omitted, it defaults to false, which will result in the current behaviour with RC=4, thus maintaining backward compatibility. In either case, a more precise message will help drastically in determining the cause of the problem. Heavily experienced mainframers do know that this situation could just be that there are no records. But less experienced sysprogs like me waste hours trying to figure out what in the world is wrong with that logstream and it's blocksize, when really it's just empty.