s.fill transformation: Prioritize string pvars over integer ones

Reason for this is that a pvar which holds a string is a more
particular occurrence than an int one, since integers can be
easily stringified.

This fixes some issues with pvars which have multiple internal
representations (e.g. $rm is "INVITE" and 1 at the same time)

Reported by Eric Tamme

transformations.c

@@ -688,12 +688,12 @@ int tr_eval_string(struct sip_msg *msg, tr_param_t *tp, int subtype,
 			/* padded final length parameter */
 			i = tp->next->v.n;
 
-			if (val->flags & PV_VAL_INT)
+			if (val->flags & PV_VAL_STR)
 			{
-				val->rs.s = int2str(val->ri, &val->rs.len);
 				i -= val->rs.len;
-			} else if (val->flags & PV_VAL_STR)
+			} else if (val->flags & PV_VAL_INT)
 			{
+				val->rs.s = int2str(val->ri, &val->rs.len);
 				i -= val->rs.len;
 			}