fix: Do not send presence unavailable after a failure.

[bgrozev]

Attempts to address jitsi/jitsi-videobridge#2052 by not sending presence
unavailable when disconnecting due to a connection failure. If the TCP
connection is alive then the server will notice that it's closed. If it
isn't alive then it won't matter anyway.

[codecov]

Codecov Report

Merging #192 (69dcf0d) into master (f49982f) will decrease coverage by 0.07%.
Report is 1 commits behind head on master.
The diff coverage is 6.89%.

@@             Coverage Diff              @@
##             master     #192      +/-   ##
============================================
- Coverage     24.05%   23.98%   -0.07%     
  Complexity      126      126              
============================================
  Files            32       32              
  Lines          1135     1138       +3     
  Branches        102      102              
============================================
  Hits            273      273              
- Misses          844      847       +3     
  Partials         18       18              

Files	Coverage Δ
...ain/kotlin/org/jitsi/config/ConfigSourceWrapper.kt	0.00% <0.00%> (ø)
...ig/src/main/kotlin/org/jitsi/config/JitsiConfig.kt	0.00% <0.00%> (ø)
.../main/java/org/jitsi/xmpp/mucclient/MucClient.java	0.00% <0.00%> (ø)
...tsi/config/AbstractReadOnlyConfigurationService.kt	25.58% <11.11%> (ø)

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