Bug 28228: Supress plugin related error message

Bug 28228: Supress plugin related error message

Use of uninitialized value in subroutine entry at /usr/share/koha/lib/Koha/Plugins/Base.pm line 182.

Test Plan:
1) Install the Kitchen Sink plugin ( it does not have a max versio defined )
2) Note the warning in your logs
3) Apply this patch
4) Restart all the things
5) No warning!

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>