ignore cache on key name change, instead of crashing
ignore cache on key name change, instead of crashing

In 6c2cf2ccdd7130a034e50f9bea481351d475a272, the names of some essential
data bits changed.  If those names are not in the tmp/apkcache, then
`fdroid update` shouldn't crash but instead just ignore that cache entry.
tmp/apkcache should be deleted since the metadata version was bumped, but
I guess that does not always happen.

fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroid-server