No trimming for fixed-length fields with empty characters in the beginning

I have some 008 fields which begin with spaces (no date data encoded). I don't know if the standard allows this, but there they are. ;) Since it's a fixed-length field with fixed character positioning, trimming from the beginning breaks e.g. language parsing.

So we could disable trimming for fixed-length fields. (my patch)

Or, maybe just switch to rtrim?