Simplify return & fshut() logic

Get rid of the !!()-constructs and use ret where available (or introduce it).

In some cases, there would be an "abort" on the first fshut-error, but we want
to close all files and report all warnings and then quit, not just the warning
for the first file.

find.c

@@ -1036,5 +1036,7 @@ main(int argc, char **argv)
 			t->u.pinfo->freearg(t->extra);
 	free(toks);
 
-	return !!(fshut(stdin, "<stdin>") + fshut(stdout, "<stdout>")) || gflags.ret;
+	gflags.ret |= fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>");
+
+	return gflags.ret;
 }