Javascript 125-ValidPalindrome.js solution is not implemented correctly

[Martin-Karsten]

As the title says the solution is not correct. There are two problems.
First it should check if the character is not alphanumeric in the while loops. The current solution checks if it is alphanumeric
Second the isAlphaNumeric method is implemented incorrectly.

[imaginate]

These problems were resolved by an earlier pull request, and the solution was further cleaned up with this commit. Thanks for opening the issue and pull request!