Do not call updateBuffer if there are no changes.

[JoeRobich]

As mentioned in this issue, microsoft/vscode#50344, the onDidChangeTextDocument callback is invoked when a document has changed as well as when its state has changed between 'dirty' and 'clean'.

When it is invoked as a state change there will be no changes and there is no need to call updateBuffer.

[filipw]

it's only a hack if we don't call it a workaround 🙂

[codecov]

Codecov Report

Merging #4170 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4170   +/-   ##
=======================================
  Coverage   85.99%   85.99%           
=======================================
  Files          60       60           
  Lines        1857     1857           
  Branches      215      215           
=======================================
  Hits         1597     1597           
  Misses        200      200           
  Partials       60       60           

Flag	Coverage Δ
integration	100.00% <ø> (ø)
unit	85.99% <ø> (ø)

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