core:parser fix possible bug in msg_parser

If buffer was NULL, tmp was returned uninitialized, thus possible to cause problems

parser/msg_parser.c

@@ -88,7 +88,7 @@ unsigned int global_req_flags = 0;
 char* get_hdr_field(char* const buf, char* const end, struct hdr_field* const hdr)
 {
 
-	char* tmp;
+	char *tmp = 0;
 	char *match;
 	struct via_body *vb;
 	struct cseq_body* cseq_b;