Correctly handle zero-length ANSI string

[kevin940726]

Currently, counting length of strings with only ansi escape codes will throw an error:

stringLength('\u001B[1m\u001B[22m');

// TypeError: Cannot read property 'length' of null

This PR fixes that by checking the length of the stripped string first.

The fix is quite straightforward. Alternatively, we can change it to something like (stripAnsi(string).match(charRegex()) || '').length (or millions of other ways).

[sindresorhus]

The initial if (string === '') { check should be preserved. It's an optimization. See recent commits in main branch.

[kevin940726]

@sindresorhus Do you mean to check it twice, one for string and the other for strippedString? Something like...

if (string === '') return 0;
const strippedString = stripAnsi(string);
if (strippedString === '') return 0;
// ...

[papb]

@kevin940726 Yes I think that's what he means

[sindresorhus]

Yes, thanks :)