ensure that user-user info field in call is properly reset when not needed

git-svn-id: https://origsvn.digium.com/svn/libpri/branches/1.2@291 2fbb986a-6c06-0410-b554-c9c1f0a7f128

q931.c

@@ -2798,6 +2798,8 @@ int q931_setup(struct pri *pri, q931_call *c, struct pri_sr *req)
 
 	if (req->useruserinfo)
 		libpri_copy_string(c->useruserinfo, req->useruserinfo, sizeof(c->useruserinfo));
+	else
+		c->useruserinfo[0] = '\0';
 
 	if (req->nonisdn && (pri->switchtype == PRI_SWITCH_NI2))
 		c->progressmask = PRI_PROG_CALLER_NOT_ISDN;