Fix: -1 can be used as a code point of most probable string.

            }

        }

        if (character != NOT_AN_INDEX) {

            codePointBuf[index] = proximityInfo->getCodePointOf(character);

            const int codePoint = proximityInfo->getCodePointOf(character);

            if (codePoint == NOT_A_CODE_POINT) {

                AKLOGE("Key index(%d) is not found. Cannot construct most probable string",

                        character);

                ASSERT(false);

                // Make the length zero, which means most probable string won't be used.

                index = 0;

                break;

            }

            codePointBuf[index] = codePoint;

            index++;

        }

        sumLogProbability += minLogProbability;