Fix counting of live sessions in session_info

[philippjfr]

If a session was established but never rendered it wouldn't count as live but still subtract from the live count.

[codecov]

Codecov Report

Merging #1634 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1634   +/-   ##
=======================================
  Coverage   85.40%   85.40%           
=======================================
  Files         147      147           
  Lines       16717    16719    +2     
=======================================
+ Hits        14277    14279    +2     
  Misses       2440     2440           

Impacted Files	Coverage Δ
panel/viewable.py	73.19% <100.00%> (+0.23%)	⬆️

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