Bug 18921: Resolve a few warnings in C4/XSLT.pm

Bug 18921: Resolve a few warnings in C4/XSLT.pm

Resolves warnings like:

Use of uninitialized value in hash element at C4/XSLT.pm line 262.
Use of uninitialized value in numeric eq (==) at C4/XSLT.pm line 267.
Use of uninitialized value $status in concatenation (.) or string at C4/XSLT.pm line 300.

Note: Line numbers are not exactly the same anymore.

Test plan:
[1] Enable XSLT view in OPAC
[2] Without this patch, you will probably have some of these warnings when
    doing some opac searches.
[3] Apply this patch. Check the logs again.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>