Fix nil pointer dereference in CompareAppState

[jessesuen]

Resolves #1233

[codecov-io]

Codecov Report

Merging #1234 into release-0.12 will increase coverage by 0.1%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           release-0.12    #1234     +/-   ##
===============================================
+ Coverage          37.3%   37.41%   +0.1%     
===============================================
  Files                59       59             
  Lines              8835     8836      +1     
===============================================
+ Hits               3296     3306     +10     
+ Misses             5039     5026     -13     
- Partials            500      504      +4

Impacted Files	Coverage Δ
controller/state.go	75% <100%> (+0.13%)	⬆️
controller/appcontroller.go	32.77% <0%> (+1.52%)	⬆️

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