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.

grep.c

@@ -277,7 +277,8 @@ main(int argc, char *argv[])
 		}
 	}
 
-	enfshut(Error, stdin, "<stdin>");
-	enfshut(Error, stdout, "<stdout>");
+	if (fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>"))
+		match = Error;
+
 	return match;
 }