uhttpd/file: fix string out of buffer range on uh_defer_script

if a url path length is multiple of 8, tailing zero will be trimed out on uh_defer_script, cause a strangle error.
it's simple to reproduce.

1. create a luci controller, register a entry with path length multiple of 8 (including '/cgi-bin/'), for example, '/cgi-bin/luci/admin/system/admin'.
2. set uhttpd max_requests to 1, and restart uhttpd
3. request '/cgi-bin/luci/admin/system/admin' with at least 2 process
4. some responses will produce a error:
```
Unable to launch the requested CGI program:
  /www/cgi-bin/luci: No such file or directory
```

Signed-off-by: Liangbin Lian <jjm2473@gmail.com>

Author: jjm2473

file.c

@@ -797,7 +797,7 @@ uh_defer_script(struct client *cl, struct dispatch_handler *d, char *url, struct
 		/* allocate enough memory to duplicate all path_info strings in one block */
 #undef _field
 #define _field(_name) &_##_name, field_len(pi->_name),
-		dr = calloc_a(sizeof(*dr), &_url, strlen(url), path_info_fields NULL);
+		dr = calloc_a(sizeof(*dr), &_url, strlen(url) + 1, path_info_fields NULL);
 
 		memcpy(&dr->pi, pi, sizeof(*pi));
 		dr->path = true;
@@ -807,7 +807,7 @@ uh_defer_script(struct client *cl, struct dispatch_handler *d, char *url, struct
 #define _field(_name) if (pi->_name) dr->pi._name = strcpy(_##_name, pi->_name);
 		path_info_fields
 	} else {
-		dr = calloc_a(sizeof(*dr), &_url, strlen(url), NULL);
+		dr = calloc_a(sizeof(*dr), &_url, strlen(url) + 1, NULL);
 	}
 
 	cl->dispatch.req_data = dr;