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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[CHOYSEN]

有任何进度吗？看起来是个没有风险的改动 @afc163@zombieJ

[afc163]

@CHOYSEN 冲突了。