Fix retrieval of HAS_FIXED_INVALID_BACKUPID setting.
Fix retrieval of HAS_FIXED_INVALID_BACKUPID setting.

The previous implementation returned false for null or empty or
whitespace values, and true for unparsable values.  A default value of
false seems more appropriate for these cases.

sitofabi/duplicati,sitofabi/duplicati,duplicati/duplicati,sitofabi/duplicati,sitofabi/duplicati,duplicati/duplicati,duplicati/duplicati,mnaiman/duplicati,mnaiman/duplicati,duplicati/duplicati,mnaiman/duplicati,mnaiman/duplicati,mnaiman/duplicati,sitofabi/duplicati,duplicati/duplicati