qisrc sync: do not crash when fetch fails

Fixes #17134

Change-Id: I8b3fe63feec59e83762777fcfadfbb4eb610d8a2
Reviewed-on: http://gerrit.aldebaran.lan/30690
Tested-by: gerrit
Reviewed-by: vbarbaresi <vbarbaresi@aldebaran-robotics.com>