MFC r275368:
When passing LUN IDs through treat ASCII values as fixed-length, not
interpreating NULLs as EOLs, but converting them to spaces.

SPC-4 does not tell that T10-based IDs should be NULL-terminated/padded.
And while it tells that it should include only ASCII chars (0x20-0x7F),
there are some USB sticks (SanDisk Ultra Fit), that have NULLs inside
the value.  Treating NULLs as EOLs there made those LUN IDs non-unique.