initilize things to quiet coverity

src/zm_regexp.cpp

@@ -49,7 +49,10 @@ RegExpr::RegExpr( const char *pattern, int flags, int p_max_matches ) : max_matc
     memset( match_lengths, 0, sizeof(*match_lengths)*max_matches );
     match_valid = new bool[max_matches];
     memset( match_valid, 0, sizeof(*match_valid)*max_matches );
+  } else {
+    match_vectors = NULL;
   }
+  match_string = "";
   n_matches = 0;
 }