[ENSCORESW-2023]. BaseMetaContainer case-sensitive for meta matching.

By default MySQL ignores differences in case and trailing spaces on varchar.
This is a change to prevent the insertion of a case sensitive variation of
an already existing meta_value. If we match exactly on the parameter, the
fuction detects the value is not present and the following insert statement
will fail since the value will be considered a duplicate.

modules/Bio/EnsEMBL/DBSQL/BaseMetaContainer.pm

@@ -398,14 +398,10 @@ sub key_value_exists {
   $sth->bind_param( 2, $value, SQL_VARCHAR );
   $sth->execute();
 
-  while ( my $arrRef = $sth->fetchrow_arrayref() ) {
-    if ( $arrRef->[0] eq $value ) {
-      $sth->finish();
-      return 1;
-    }
-  }
+  return 0 unless $sth->fetchrow_arrayref();
+
+  return 1;
 
-  return 0;
 } ## end sub key_value_exists
 
 # This utility method determines whether the key is a species-specific