Fix bug: body can be empty in POST/PATCH request in actions

[Pierre-Gilles]

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Description of change

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[codecov]

Codecov Report

Merging #1072 (3ac6d71) into master (1d8005c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1072   +/-   ##
=======================================
  Coverage   95.22%   95.22%           
=======================================
  Files         525      525           
  Lines        6968     6968           
=======================================
  Hits         6635     6635           
  Misses        333      333           

Impacted Files	Coverage Δ
server/lib/scene/scene.actions.js	96.10% <100.00%> (ø)

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