custom mask incorrect logic on deletion of character before a delimiter

[rsouthgate]

Take a mask 999-999 for example.

Input the text 123456 which is translated to 123-456.

Position caret before delimiter: 123|-456 and delete; 12-456

The logic on the custom mask to replace the characters here:

var translationHandler = translation[maskChar];
    if (translationHandler) {
      var resolverValue = translationHandler(valueChar || '');
      if (resolverValue !== null) {
        result += resolverValue;
        valueCharIndex += 1;
      } else {
        result += maskChar;
      }
      maskCharIndex += 1;
      continue;
    }
    result += maskChar;
    maskCharIndex += 1;
    continue;

after the deletion when it meets character 3 ('-') with the mask character 3 ('9') will replace with '' and move to character 4 ('4') and compare with mask character 4 ('-') for which there is no translation handler so the result gets the mask character ('-').

I have modified this in a fork and will submit a PR referencing this issue.