fix: add try and catch for computedStyle

[weiz18]

Description

With shadow root enable component, computedStyle gets called on dragging the progress bar. and since we are traversing the path back to the top, if you have a shadow root component in the path, it will try to call computeStyle for shadow root (document fragment) which will then cause the following error
Uncaught TypeError: Failed to execute 'getComputedStyle' on 'Window': parameter 1 is not of type 'Element'.

video.js/src/js/utils/dom.js

Line 620 in 4238f5c

while (item && item.nodeName.toLowerCase() !== 'html') {

Specific Changes proposed

Adding try and catch so the code can continue to run despite the error

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

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[gkatsev]

Thanks. LGTM, just one stylistic nit.

[welcome]

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