Do not add PENDING_WRITES to the queue if future is DONE

[violetagg]

When adding to the queue is scheduled operation, check again whether
future is DONE and there are pending write bytes.

[codecov-io]

Codecov Report

Merging #445 into 0.7.x will increase coverage by 0.36%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##             0.7.x     #445      +/-   ##
===========================================
+ Coverage     68.1%   68.46%   +0.36%     
- Complexity    1054     1058       +4     
===========================================
  Files           73       73              
  Lines         4512     4513       +1     
  Branches       653      654       +1     
===========================================
+ Hits          3073     3090      +17     
+ Misses        1048     1034      -14     
+ Partials       391      389       -2

Impacted Files	Coverage Δ	Complexity Δ
...or/ipc/netty/channel/ChannelOperationsHandler.java	65.79% <0%> (+0.94%)	60 <0> (ø)	⬇️
...or/ipc/netty/http/client/HttpClientOperations.java	56.73% <0%> (+0.25%)	81% <0%> (+1%)	⬆️
...ctor/ipc/netty/resources/DefaultPoolResources.java	79.38% <0%> (+3.09%)	9% <0%> (+1%)	⬆️
.../ipc/netty/channel/PooledClientContextHandler.java	71.42% <0%> (+4.2%)	28% <0%> (+1%)	⬆️
.../ipc/netty/http/server/HttpServerWSOperations.java	68.42% <0%> (+5.26%)	15% <0%> (+1%)	⬆️

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