TT#33356 Rewrite rule validation checks for ambiguous non-char escapes

* Sequences with escaping a non-special char in the search pattern
      like \43699 or \abc are now checked and prohibited

Change-Id: I72d65f2dbf5b9b9bae1ff37af098d74d238f77cb
(cherry picked from commit d045b35b3c)

lib/NGCP/Panel/Form/RewriteRule/Rule.pm

@@ -151,6 +151,10 @@ sub validate {
         $self->field('replace_pattern')->add_error("Spaces are not allowed in replacement pattern");
     }
 
+    if ( $s =~ /\\\w/i ) {
+        $self->field('match_pattern')->add_error("Ambiguous escape of non special characters");
+    }
+
     my @acount;
     @acount = $s =~ /(\@\{\w+\})/g;
     if(@acount > 1) {