Skip extra heartbeats when no data provided

[gandarez]

This PR fixes reading extra heartbeat when the flag is set to true but no data was provided.

current log

failed to read extra heartbeats: failed parsing: failed to json decode from data \"\": unexpected end of JSON input

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e983264) 62.95% compared to head (eed6d94) 62.96%.

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@@             Coverage Diff             @@
##           develop    #1022      +/-   ##
===========================================
+ Coverage    62.95%   62.96%   +0.01%     
===========================================
  Files          374      374              
  Lines        15960    15965       +5     
===========================================
+ Hits         10048    10053       +5     
  Misses        5378     5378              
  Partials       534      534              

Flag	Coverage Δ
unittests	62.96% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
cmd/params/params.go	85.96% <100.00%> (+0.09%)	⬆️

[alanhamlett]

Good catch. So this only resulted in an error logged, but the main heartbeat was still sent to the api and not lost. It's good this cleans up the ~/.wakatime/wakatime.log so it's not noisy.