Bug 13991: Uninitialized value $src in /tools/viewlog.pl

Bug 13991: Uninitialized value $src in /tools/viewlog.pl

To reproduce:

Go to Home > Tools > Logs
Check intranet-error.log.
You will find a line similar to:
viewlog.pl: Use of uninitialized value $src in string eq at (...)/tools/viewlog.pl line 70., referer: http://(...)/cgi-bin/koha/tools/tools-home.pl

To test:
Apply patch.
Verify that no more warnings appear in intranet-error.log
Verify that the log viewer behaves as before.

Signed-off-by: Andreas Hedström Mace <andreas.hedstrom.mace@sub.su.se>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
(cherry picked from commit 7ec3d6dfe98e19f0baa525a5b2b3839b0a35379c)
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>