tr: Fix infinite loop

When `makeset` got a string containing square brackets
followed by at least one extra character, e.g. "[abc]d",
it entered an infinite loop because it was assumed
`j` could not exceed `len` without having been equal to `len`.
It can, however, when `m == len` and subsequently `j = m + 1`.

tr.c

@@ -85,7 +85,7 @@ makeset(char *str, struct range **set, int (**check)(Rune))
 		if (rstr[i] == '[') {
 			j = i;
 nextbrack:
-			if (j == len)
+			if (j >= len)
 				goto literal;
 			for (m = j; m < len; m++)
 				if (rstr[m] == ']') {