passt-repair: Ensure that read buffer is NULL-terminated

After 3d41e4d838 ("passt-repair: Correct off-by-one error verifying
name"), Coverity Scan isn't convinced anymore about the fact that the
ev->name used in the snprintf() is NULL-terminated.

It comes from a read() call, and read() of course doesn't terminate
it, but we already check that the byte at ev->len - 1 is a NULL
terminator, so this is actually a false positive.

In any case, the logic ensuring that ev->name is NULL-terminated isn't
necessarily obvious, and additionally checking that the last byte in
the buffer we read is a NULL terminator is harmless, so do that
explicitly, even if it's redundant.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

passt-repair.c

@@ -137,6 +137,7 @@ int main(int argc, char **argv)
 				fprintf(stderr, "inotify read: %i", errno);
 				_exit(1);
 			}
+			buf[n - 1] = '\0';
 
 			if (n < (ssize_t)sizeof(*ev)) {
 				fprintf(stderr, "Short inotify read: %zi", n);