Run(): clear previous timer id if needed

[tobast]

Fixes #1196

All tests passing:

$ make test
[...]
Total: 189 tests (85447 ticks, 0.085 sec), 2430 assertions
Pass: 189, fail: 0, skip: 0.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 66.10%. Comparing base (d314806) to head (e2329b4).
Report is 183 commits behind head on master.

Files	Patch %	Lines
src/dunst.c	0.00%	5 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1257      +/-   ##
==========================================
- Coverage   66.17%   66.10%   -0.07%     
==========================================
  Files          46       46              
  Lines        7696     7701       +5     
==========================================
- Hits         5093     5091       -2     
- Misses       2603     2610       +7     

Flag	Coverage Δ
unittests	66.10% <0.00%> (-0.07%)	⬇️

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[fwsmit]

Thanks for the quick fix and taking responsibility for your code :). The fix looks good, so I'll go ahead and merge