SVGHMI: Fix browser side exception when some widget are not used, and are then discarded and not present in final SVG. In that case JS code was still making reference to discarded widget elements and was raising exception at init.

[TOPOLOGY]
NetName=None
Nodes=0x01
Node2Present=0x01
Node2Name=SlaveNode
Node2DCFName=Slave_0_0.eds
EDSBaseName=eds