Don't terminate when statfs() fails.

[delphij]

Summary

Current code terminates when statfs() fails, in -fstype
primary, which can happen when a directory is removed in the middle
of find.

Instead of a full err(), treat this as an error that can continue
by returning 0.

[jilles]

Hmm, looking again, the idea of continuing is good, but printing diagnostics without affecting the exit status is usually not POSIX-compliant. To fix this, the global variable exitstatus can be set to 1. Note that there are existing places in function.c that do this wrong (which need not be fixed for this review).

Also, if the error is ENOENT and the global variable ignore_readdir_race is set, both diagnostic and exit status change need not happen.

[delphij]

Address jilles's comments.