don't fail loading releases if a referenced user doesn't exist
don't fail loading releases if a referenced user doesn't exist

this was failing on staging where not all users are copied over

dimagi/commcare-hq,SEL-Columbia/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,puttarajubr/commcare-hq,gmimano/commcaretest,qedsoftware/commcare-hq,SEL-Columbia/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,gmimano/commcaretest,puttarajubr/commcare-hq,qedsoftware/commcare-hq,gmimano/commcaretest,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq