Convert find_alnum_point to find the first non-whitespace point

This is a small fix to support languages other than Python with cleaning code completions up to the end of the target block.

Prompt:

const newFunctionForValidatingEmail = (email) => {
  return emailRegex.test(email);
<cursor>

Before:

Output:

}

const newFunctionForValidatingPassword = (password) => {
  return passwordRegex.test(password);
};

After:

Output:

};

Ref - #273 (comment 1534115338).