Move variable declarations to the top

This should fix the CI issues with Visual Studio 2010 and 2012.

src/handle_form.inl

@@ -184,13 +184,13 @@ mg_handle_form_request(struct mg_connection *conn,
 	int64_t file_size = 0; /* init here, to a avoid a false positive
 	                         "uninitialized variable used" warning */
 
+	int has_body_data =
+	    (conn->request_info.content_length > 0) || (conn->is_chunked);
+
 	/* Unused without filesystems */
 	(void) fstore;
 	(void) file_size;
 
-	int has_body_data =
-	    (conn->request_info.content_length > 0) || (conn->is_chunked);
-
 	/* There are three ways to encode data from a HTML form:
 	 * 1) method: GET (default)
 	 *    The form data is in the HTTP query string.