HTTP parser: restricting allowed characters in fields values.

According to RFC 7230 only printable 7-bit ASCII characters are allowed
in field values.

src/test/nxt_http_parse_test.c

@@ -280,6 +280,24 @@ static nxt_http_parse_test_case_t  nxt_http_test_cases[] = {
         NXT_HTTP_PARSE_INVALID,
         NULL, { NULL }
     },
+    {
+        nxt_string("GET / HTTP/1.1\r\n"
+                   "Host: exa\bmple.com\r\n\r\n"),
+        NXT_HTTP_PARSE_INVALID,
+        NULL, { NULL }
+    },
+    {
+        nxt_string("GET / HTTP/1.1\r\n"
+                   "Host: пример.испытание\r\n\r\n"),
+        NXT_HTTP_PARSE_INVALID,
+        NULL, { NULL }
+    },
+    {
+        nxt_string("GET / HTTP/1.1\r\n"
+                   "Host: xn--e1afmkfd.xn--80akhbyknj4f\r\n\r\n"),
+        NXT_DONE,
+        NULL, { NULL }
+    },
     {
         nxt_string("GET / HTTP/1.1\r\n"
                    "X-Unknown-Header: value\r\n"