src: put `assert()` after var declarations

Microsoft C++ compiler fails when this assert appears before the
declarations. Moved assert to appear after the declarations.

PR-URL: https://github.com/nodejs/http-parser/pull/293
Reviewed-By: Fedor Indutny <fedor@indutny.com>

http_parser.c

@@ -2253,12 +2253,13 @@ http_parse_host_char(enum http_host_state s, const char ch) {
 
 static int
 http_parse_host(const char * buf, struct http_parser_url *u, int found_at) {
-  assert(u->field_set & (1 << UF_HOST));
   enum http_host_state s;
 
   const char *p;
   size_t buflen = u->field_data[UF_HOST].off + u->field_data[UF_HOST].len;
 
+  assert(u->field_set & (1 << UF_HOST));
+
   u->field_data[UF_HOST].len = 0;
 
   s = found_at ? s_http_userinfo_start : s_http_host_start;