Updated fix for major bug EXT-6786 ('Stand' button is corrupted if movement...

Updated fix for major bug EXT-6786 ('Stand' button is corrupted if movement control floater is opened)

Added force hiding of Stand button to avoid seeing Stand & Move buttons at once for a short moment.

Reviewed by Vadim Savchuk at https://codereview.productengine.com/secondlife/r/233/

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branch : product-engine