_WD_GetElementFromPoint: Detect invalid coordinates

[Danp2]

Pull request

Proposed changes

Return additional error code to indicate invalid parameters.

Checklist

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• I have read and noticed the CODE OF CONDUCT document
• I have read and noticed the CONTRIBUTING document
• I have added necessary documentation or screenshots (if appropriate)

Types of changes

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• Bugfix (change which fixes an issue)
• Feature (change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (functional, structural)
• Documentation content changes
• Other (please describe)

What is the current behavior?

Empty string is returned, but no error code is generated

What is the new behavior?

Sets @err to $_WD_ERROR_InvalidArgue if a negative coordinate is detected

Additional context

Add any other context about the problem here.

System under test

Please complete the following information.

• OS: [e.g. Windows 10]
• OS Arch.: [e.g. X64]
• Browser [e.g. firefox]
• Browser version [e.g. 96.0.3]

[mlipok]

Looks good as so far.