Bug 11127: OPAC suggestions form - complain when trying to 'delete selected' without...

Bug 11127: OPAC suggestions form - complain when trying to 'delete selected' without having selected any

To reproduce:
1/ go on opac-suggestions.pl
2/ create a suggestion
3/ click on the delete link without checking any checkbox
The form is submitted with a message "The selected suggestions have been
deleted.".

Test plan:
0/ enable the bootstrap theme
1/ after applying the patch, click on delete without any checkbox
checked, a js alert should occur.
2/ check at least a cb and click on the delete link. The deletion should
work.

Followed test plan. Patch behaves as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script, works as described.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit b02f40d6e1febc0802b82660c56f1745ea664fd5)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>