#513 psradd fails to use existing predictors from the input files

[Stepan Andrianov]

After applying time corrections through "psredit -c ext:stt_offs=..." the profile becomes off the null phase. After, when using psradd it tries to align the profiles but fails to use existing predictors and generates a new using tempo2. This significantly increases the processing time even when the existing file's predictor is valid.