Fix conversion from uint256 to string

contracts/utils/Strings.sol

@@ -10,25 +10,29 @@ library Strings {
      * @dev Converts a `uint256` to its ASCII `string` representation.
      */
     function toString(uint256 value) internal pure returns (string memory) {
-        // Inspired by OraclizeAPI's implementation - MIT licence
-        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol
-
         if (value == 0) {
             return "0";
         }
+
         uint256 temp = value;
         uint256 digits;
         while (temp != 0) {
             digits++;
             temp /= 10;
         }
-        bytes memory buffer = new bytes(digits);
-        uint256 index = digits - 1;
-        temp = value;
-        while (temp != 0) {
-            buffer[index--] = bytes1(uint8(48 + temp % 10));
-            temp /= 10;
+        bytes memory reversed = new bytes(digits + 1);
+        uint256 i = 0;
+        while (value != 0) {
+            uint256 remainder = value % 10;
+            value /= 10;
+            reversed[i++] = bytes1(uint8(48 + remainder));
         }
+
+        bytes memory buffer = new bytes(i);
+        for (uint256 j = 1; j <= i ; j++) {
+            buffer[j - 1] = reversed[i - j];
+        }
+
         return string(buffer);
     }
 }