r1969 merge:

fix segfault

src/http/ngx_http_upstream.c

@@ -2543,6 +2543,10 @@ ngx_http_upstream_copy_content_type(ngx_http_request_t *r, ngx_table_elt_t *h,
 
         while (*++p == ' ') { /* void */ }
 
+        if (*p == '\0') {
+            return NGX_OK;
+        }
+
         if (ngx_strncasecmp(p, (u_char *) "charset=", 8) != 0) {
             continue;
         }