Fix bug in TOC file error message printing

Fix bug in TOC file error message printing

If the blob TOC file cannot be parsed, the error message was failing
to print the filename as the variable holding it was shadowed by the
destination buffer for parsing.  When the filename fails to parse,
the error will print an empty string:

 ./pg_restore -d foo -F d dump
 pg_restore: error: invalid line in large object TOC file "": ..

..instead of the intended error message:

 ./pg_restore -d foo -F d dump
 pg_restore: error: invalid line in large object TOC file "dump/blobs.toc": ..

Fix by renaming both variables as the shared name was too generic to
store either and still convey what the variable held.

Backpatch all the way down to 9.6.

Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/A2B151F5-B32B-4F2C-BA4A-6870856D9BDE@yesql.se
Backpatch-through: 9.6