Derive maximum base from number of digits instead of hardcoding

baseconv.c

@@ -9,7 +9,7 @@ static const char digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
 bool baseconv(char outbuf[], size_t bufsize, unsigned base, uintmax_t num) {
 	// Supported bases are 2 to 36 inclusive (though it could be higher
 	// if our digits string was longer
-	if (base < 2 || base > 36)
+	if (base < 2 || base > sizeof(digits))
 		return false;
 
 	// Longest possible converted string is base-2, where we produce one