Bug 15130: useless unitialization warnings when updating authorities

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
  Fixes a trivial coding error.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

C4/AuthoritiesMarc.pm

@@ -1515,7 +1515,7 @@ sub merge {
     # BulkEdit marc records
     # May be used as a template for a bulkedit field  
     foreach my $marcrecord(@reccache){
-        my $update;           
+        my $update = 0;
         foreach my $tagfield (@tags_using_authtype){
 #             warn "tagfield : $tagfield ";
             foreach my $field ($marcrecord->field($tagfield)){