fix(throttle): fix issue #709, where throttled Stream does not emit done event.

[hoc081098]

…one event.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.31%. Comparing base (e8ad800) to head (93f29d3).
⚠️ Report is 121 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #710   +/-   ##
=======================================
  Coverage   93.30%   93.31%           
=======================================
  Files          77       77           
  Lines        2390     2392    +2     
=======================================
+ Hits         2230     2232    +2     
  Misses        160      160           

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[hoc081098]

@frankpepermans I'm not sure this change is correct. Could you review it, please? Thanks 👍