Fix event converting when previous_instance_count is not provided

[PlamenDoychev]

No description provided.

[cfdreddbot]

✅ Hey PlamenDoychev! The commit authors and yourself have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/162727617

The labels on this github issue will be updated when the story is started.

[codecov]

Codecov Report

Merging #1143 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1143   +/-   ##
=======================================
  Coverage   95.22%   95.22%           
=======================================
  Files         126      126           
  Lines        3479     3479           
=======================================
  Hits         3313     3313           
  Misses        166      166

Impacted Files	Coverage Δ
lib/cf/applications/src/app-event-converter.js	100% <ø> (ø)	⬆️

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No real-life scenario