fix: NPE on onClusterItemUpdated

[arriolac]

Attempt to fix NPE in onClusterItemUpdated by swapping the method invocation on the ClusterItem vs. the Marker.
This should work since a null check was performed prior to invoking methods on it.

I couldn't quite repro the crash myself (I was modifying ClusteringDemoActivity locally to try to repro) though.

@barbeau if you have any ideas how to repro this I'm happy to check that.

Fixes #673

[codecov]

Codecov Report

Merging #675 into master will not change coverage by %.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #675   +/-   ##
=======================================
  Coverage   39.35%   39.35%           
=======================================
  Files          71       71           
  Lines        4035     4035           
  Branches      606      606           
=======================================
  Hits         1588     1588           
  Misses       2344     2344           
  Partials      103      103           

Impacted Files	Coverage Δ
...ndroid/clustering/view/DefaultClusterRenderer.java	0.00% <0.00%> (ø)

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[barbeau]

Thanks @arriolac! Yes, this is the proper fix.