Fix bugs in RateLimiterController

[mjaow]

Describe what this PR does / why we need it

Fix bugs when count is zero

when count is zero,the costTime value will be max of long.After some retries of canPass,the waitTime will overflow and permit any request (as it will return true)

Does this pull request fix one issue?

Fixes #462

Describe how you did it

precheck and return when acquire count or count is less or equal than zero

Describe how to verify it

Test case in RateLimiterControllerTest.testPaceController_zeroattack

Special notes for reviews

The bug will lead to attack and make limiter useless

[codecov-io]

Codecov Report

Merging #461 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #461      +/-   ##
============================================
+ Coverage     37.62%   37.62%   +<.01%     
- Complexity      982      983       +1     
============================================
  Files           235      235              
  Lines          7429     7433       +4     
  Branches       1017     1018       +1     
============================================
+ Hits           2795     2797       +2     
- Misses         4273     4274       +1     
- Partials        361      362       +1

Impacted Files	Coverage Δ	Complexity Δ
...s/block/flow/controller/RateLimiterController.java	79.31% <100%> (+3.31%)	7 <5> (+2)	⬆️
...a/csp/sentinel/slots/statistic/base/LeapArray.java	62.02% <0%> (-2.54%)	22% <0%> (-1%)

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[sczyh30]

Hi, thanks for contributing. The zero-count problem is a bug (thanks for fixing that).

As for RateLimiterController, it is designed as a not strictly thread-safe implementation for performance (as well as in other traffic controllers). In Sentinel we need to consider both correctness and performance.

[mjaow]

ok,i'll keep the bugfix part and delete the commit which fix concurrent issue and reference annother issue to discuss it

[sczyh30]

LGTM

[sczyh30]

Thanks for contributing!