some APKs do not have a name, like system APKs

It is not necessarily a good idea to try to distribute system APKs via
FDroid, but `fdroid update` should just ignore APKs it cannot handle rather
than die and prevent a repo from being fully created.  This is necessary to
handle the automatic creation of repos, like for debug builds from a
Jenkins server.

fdroidserver/update.py

@@ -967,6 +967,9 @@ def main():
                 break
         if not found:
             if options.create_metadata:
+                if 'name' not in apk:
+                    logging.error(apk['id'] + ' does not have a name! Skipping...')
+                    continue
                 f = open(os.path.join('metadata', apk['id'] + '.txt'), 'w')
                 f.write("License:Unknown\n")
                 f.write("Web Site:\n")