Fixed bug with MapView extension _showInfoWindow() function
Fixed bug with MapView extension _showInfoWindow() function

The onclick function called the _showInfoWindow() function without
any marker, resulting in an undefined marker variable, meaning that
marker.getIcon() would throw a runtime error when looking for
marker size. As a result, this prevented onclick labeling from
working.

We only set markerSize now when there is a defined marker variable.

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