fix(filter): refreshTreeDataFilters only when Tree is enabled fixes #806

[ghiscoding]

• also make sure DataView object exist before trying to get items array
• quick fixes #806

[codecov]

Codecov Report

Merging #807 (d30b330) into version2 (481cfc6) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           version2      #807   +/-   ##
==========================================
  Coverage    100.00%   100.00%           
==========================================
  Files           162       162           
  Lines         11348     11350    +2     
  Branches       4055      4057    +2     
==========================================
+ Hits          11348     11350    +2     

Impacted Files	Coverage Δ
...dules/angular-slickgrid/services/filter.service.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 481cfc6...d30b330. Read the comment docs.