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[bot]]

Codecov Report

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

:exclamation: 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%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 55ed22f...b2de5d2. Read the comment docs.