fix: error on undefined metadata frames

[adrums86]

Description

Fixes an issue where an error is thrown when the frame of timed metadata is undefined

Specific Changes proposed

Add a check for !metadata.frames || !metadata.frames.length with an early return to the addMetadata function.

Requirements Checklist

• [x] Feature implemented / Bug fixed
• [ ] If necessary, more likely in a feature request than a bug fix
  • [ ] Unit Tests updated or fixed
  • [ ] Docs/guides updated
  • [ ] Example created (starter template on JSBin)
• [ ] Reviewed by Two Core Contributors

[codecov[bot]]

Codecov Report

Merging #1383 (a22c58c) into main (915bdee) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1383   +/-   ##
=======================================
  Coverage   85.35%   85.36%           
=======================================
  Files          40       40           
  Lines        9951     9953    +2     
  Branches     2306     2307    +1     
=======================================
+ Hits         8494     8496    +2     
  Misses       1457     1457           

Impacted Files	Coverage Δ
src/util/text-tracks.js	86.53% <100.00%> (+0.26%)	:arrow_up:

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