blaze822: don't try to open /dev/stdin

Use the same check is blaze822() as in blaze822_file() to ensure that
we don't try to open /dev/stdin, which is non-POSIX.
Message-Id: <20220523170921.2623516-1-hi@alyssa.is>

blaze822.c

@@ -443,7 +443,10 @@ blaze822(char *file)
 	if (!mesg)
 		return 0;
 
-	fd = open(file, O_RDONLY);
+	if (strcmp(file, "/dev/stdin") == 0)
+		fd = dup(0);
+	else
+		fd = open(file, O_RDONLY);
 	if (fd < 0) {
 		free(mesg);
 		return 0;