avoid segfault caused by user error

If the CALLERPRES() dialplan function is set to nothing,
a segfault occurs.  This is user error to begin with, but
I'd rather see a cli warning message than have Asterisk
crash on me.



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@206867 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/callerid.c

@@ -1092,6 +1092,10 @@ int ast_parse_caller_presentation(const char *data)
 {
 	int i;
 
+	if (!data) {
+		return -1;
+	}
+
 	for (i = 0; i < ((sizeof(pres_types) / sizeof(pres_types[0]))); i++) {
 		if (!strcasecmp(pres_types[i].name, data))
 			return pres_types[i].val;