core: Cancel gdata_download_stream_read() if the entire download is cancelled
core: Cancel gdata_download_stream_read() if the entire download is cancelled

Helps: bgo#637036

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