fix: Cannot read property appendBuffer of undefined

[xiaoyuhen]

fix: Cannot read property appendBuffer of undefined

Description

Fixes #47

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[codecov-io]

Codecov Report

Merging #48 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master      #48   +/-   ##
=======================================
  Coverage   52.98%   52.98%           
=======================================
  Files         123      123           
  Lines        1659     1659           
=======================================
  Hits          879      879           
  Misses        780      780

Impacted Files	Coverage Δ
packages/griffith-mp4/src/mse/controller.js	0% <0%> (ø)	⬆️

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