check mouseDownTimeout timer before calling clearTimeout

[shc023]

this PR boosts performance in our React App, when unmounting a large list containing 10k+ rc-tooltips

[codecov]

Codecov Report

Merging #278 (bd89a0e) into master (55ed22f) will decrease coverage by 0.09%.
The diff coverage is 83.33%.

❗ Current head bd89a0e differs from pull request most recent head b2de5d2. Consider uploading reports for the commit b2de5d2 to get more accurate results

@@            Coverage Diff             @@
##           master     #278      +/-   ##
==========================================
- Coverage   89.88%   89.79%   -0.10%     
==========================================
  Files          11       11              
  Lines         534      539       +5     
  Branches      136      137       +1     
==========================================
+ Hits          480      484       +4     
- Misses         54       55       +1     

Impacted Files	Coverage Δ
src/index.tsx	86.57% <83.33%> (-0.10%)	⬇️

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