fix(editors): AutoComplete Editor might have undefined object label

[ghiscoding]

• it was throwing an error when the item dataContext did not have the label (or custom label) property inside the item dataContext

[codecov]

Codecov Report

Merging #555 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #555    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          148       148            
  Lines         9719      9719            
  Branches      3274      3414   +140     
==========================================
  Hits          9719      9719            

Impacted Files	Coverage Δ
...es/angular-slickgrid/editors/autoCompleteEditor.ts	100.00% <100.00%> (ø)

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