contentenc: downgrade "interrupted write?" warning to debug
contentenc: downgrade "interrupted write?" warning to debug

This can happen during normal operation, and is harmless since

14038a1644f17f50b113a05d09a2a0a3b3e973b2
"fusefrontend: readFileID: reject files that consist only of a header"

causes dormant header-only files to be rewritten on the next write.

rfjakob/gocryptfs,davesteele/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs