Fix XHR abort and complete event firing

Ensure the fetch aborts immediately if Uppy is cancelled before the fetch starts.

Author: mifi

.changeset/afraid-beers-listen.md

@@ -0,0 +1,6 @@
+---
+"@uppy/utils": patch
+"@uppy/xhr-upload": patch
+---
+
+Fix `complete` event never firing for XHR and make sure the fetch aborts immediately if Uppy is cancelled before the fetch starts.