fix length of array is never negative

[tswstarplanet]

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[codecov-io]

Codecov Report

Merging #4510 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #4510      +/-   ##
============================================
- Coverage     62.94%   62.91%   -0.03%     
- Complexity      449      450       +1     
============================================
  Files           770      770              
  Lines         33006    33006              
  Branches       5216     5216              
============================================
- Hits          20774    20766       -8     
- Misses         9835     9845      +10     
+ Partials       2397     2395       -2

Impacted Files	Coverage Δ	Complexity Δ
...o/common/extension/support/ActivateComparator.java	66.66% <100%> (ø)	0 <0> (ø)	⬇️
...ache/dubbo/remoting/p2p/support/AbstractGroup.java	45.45% <0%> (-11.37%)	0% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	61.17% <0%> (-4.71%)	0% <0%> (ø)
...he/dubbo/remoting/transport/netty/NettyServer.java	69.64% <0%> (-3.58%)	8% <0%> (-1%)
...pache/dubbo/registry/support/AbstractRegistry.java	78.54% <0%> (-3.07%)	0% <0%> (ø)
.../exchange/support/header/HeaderExchangeServer.java	65.09% <0%> (-1.89%)	0% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	59.48% <0%> (-0.37%)	0% <0%> (ø)
...ache/dubbo/registry/multiple/MultipleRegistry.java	63.38% <0%> (+0.7%)	21% <0%> (+1%)	⬆️
...che/dubbo/remoting/transport/mina/MinaChannel.java	55.26% <0%> (+1.31%)	18% <0%> (+1%)	⬆️
...he/dubbo/registry/multicast/MulticastRegistry.java	69.23% <0%> (+1.35%)	0% <0%> (ø)	⬇️
... and 3 more

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[htynkn]

According to doc (https://docs.oracle.com/javase/specs/jls/se8/html/jls-10.html#jls-10.7), length may be positive or zero.

Also when try to create a negative length array, it will throw NegativeArraySizeException