core: Cancel gdata_upload_stream_write() if the entire upload is cancelled
core: Cancel gdata_upload_stream_write() if the entire upload is cancelled

Helps: bgo#637036

Pecisk/libgdata,Distrotech/libgdata,pwithnall/libgdata,Distrotech/libgdata,Pecisk/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata-gtasks,GNOME/libgdata,Pecisk/libgdata-gtasks,Distrotech/libgdata,pwithnall/libgdata