util/spkmodem-recv: warn on unhandled exit error

my style of C programming is this: always return errno
upon exit from the program, or from a thread.

handle errno in the calling/forking function.

returning errno at the end of main has this intention:
if an unhandled error occured, the program exits with
non-zero status.

a correctly written program should *never* return non-zero
at the end of main, and if it does, this indicates a bug
in the code (per my code style / philosophy).

so, warn the user with a message if this occurs. the
intention is that this message should never be printed.

do not use assert() for this. i don't believe in that.
such a test should always be present, for everyone.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/spkmodem_recv/spkmodem-recv.c

@@ -56,7 +56,9 @@ main(int argc, char *argv[])
 	while (!feof(stdin))
 		handle_audio();
 
-	return errno;
+	if (errno)
+		err(errno, "Unhandled error upon exit. Exit status is errno.");
+	return 0;
 }
 
 void