xz: Refactor suffix test with raw format.

The previous version set opt_stdout, but this caused an issue with
copying an input file to standard out when decompressing an unknown file
type. The following needs to result in an error:

    echo foo | xz -df

since -c, --stdout is not used. This fixes the previous error by not
setting opt_stdout.

src/xz/args.c

@@ -834,34 +834,22 @@ args_parse(args_info *args, int argc, char **argv)
 		args->arg_count = (unsigned int)(argc - optind);
 	}
 
-	// If all of the filenames provided are "-" (more than one "-"
-	// could be specified) or no filenames are provided, then we are
-	// only going to be writing to standard out. However if --files or
-	// --files0 is used, then we will not be writing to standard out.
-	if (!opt_stdout && args->files_name == NULL) {
-		uint32_t i;
-
-		for (i = 0; i < args->arg_count; i++) {
-			const char *name = args->arg_names[i];
-
-			// getopt_long() will not give us an empty string
-			// as an argument name here so we don't need to
-			// check if name[0] is a NULL terminator.
-			if (name[0] != '-' && name[1] != '\0')
-				break;
-		}
-
-		// Set opt_stdout if the loop did not exit early.
-		opt_stdout = i == args->arg_count;
-	}
-
 	// If raw format is used and a custom suffix is not provided,
-	// then only stdout mode can be used when compressing or decompressing.
+	// then only stdout mode can be used when compressing or
+	// decompressing.
 	if (opt_format == FORMAT_RAW && !suffix_is_set() && !opt_stdout
 			&& (opt_mode == MODE_COMPRESS
-				|| opt_mode == MODE_DECOMPRESS))
-		message_fatal(_("With --format=raw, --suffix=.SUF is "
-				"required unless writing to stdout"));
+				|| opt_mode == MODE_DECOMPRESS)) {
+		// If all of the filenames provided are "-" (more than one
+		// "-" could be specified) or no filenames are provided,
+		// then we are only going to be writing to standard out.
+		for (unsigned int i = 0; i < args->arg_count; i++) {
+			if (strcmp(args->arg_names[i], "-") != 0)
+				message_fatal(_("With --format=raw, "
+						"--suffix=.SUF is required "
+						"unless writing to stdout"));
+		}
+	}
 
 	return;
 }