Bug 23045: TextMarc errors on blank lines

Bug 23045: TextMarc errors on blank lines

Since bug 16251 we use TextMarc to get some record fields, however, it throws an error when
processing blank lines.

We should just pass on these rather then erroring

To test:
1 - Define a new macro that delete more fields than it adds
  delete 245
2 - Run it
3 - Note an error in JS console, and helpers will not load
4 - Apply patch
5 - Reload, try again
6 - No error

Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>