Fixed UIContext leak when jetty fails to close a websocket

[anthony-maire]

With older versions of jetty (9.4.6) we already observed that is possible to be called from the "onWebSocketClose()" callback, but we finished with the session still open because of an exception in a listener

[codecov]

Codecov Report

Merging #255 into master will increase coverage by 0.01%.
The diff coverage is 8.88%.

@@             Coverage Diff              @@
##             master     #255      +/-   ##
============================================
+ Coverage     20.98%   20.99%   +0.01%     
- Complexity     1111     1112       +1     
============================================
  Files           397      397              
  Lines         14447    14446       -1     
  Branches       1694     1693       -1     
============================================
+ Hits           3031     3033       +2     
+ Misses        11185    11181       -4     
- Partials        231      232       +1

Impacted Files	Coverage Δ	Complexity Δ
...ponysdk/core/server/websocket/WebSocketPusher.java	1.61% <0%> (+0.06%)	2 <0> (ø)	⬇️
...main/java/com/ponysdk/impl/main/PonySDKServer.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...com/ponysdk/core/server/application/UIContext.java	43.9% <100%> (+1.9%)	36 <1> (+1)	⬆️
...m/ponysdk/core/server/application/Application.java	81.25% <40%> (-5.71%)	17 <2> (ø)
...a/com/ponysdk/core/server/websocket/WebSocket.java	66.66% <8.33%> (-2.86%)	35 <1> (ø)

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