[INTERNAL] prevent rare NPE in IPN

project.findMember() may return null for resources that does not exists.
Although we have written them to disk before this call must not mean
that all data is still present.

Change-Id: I29b1c868adb1c3b04c9db5a2f81a3e0f44716fd8
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1928
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>