fix: fix getCurrentScriptSource to handle scripts without src

[tinytinyeye]

The current implementation of getCurrentScriptSource will fail when there are scripts without src used in the document and the script that runs React app is not the last script in the document.

For example, in the case when there are other 3rd party script snippets such as Qualtrics used in the document, the last script get by the original implementation could be such script and the src will be null. As a result, getCurrentScriptSource will return null and getSocketUrlParts will fail at url.parse(scriptSource || '').

To fix this issue, we could return the last script that HAS src attribute as the current script.

[nticaric]

If the changes in #323 go through this will be automatically fixed

[tinytinyeye]

Hey @pmmmwh, recently I updated my commits to include the changes you suggested and was wondering if you still have other concerns regarding my fix. Thank you!