ExpressionUI : Fix bug going from good->bad->same good expression.
ExpressionUI : Fix bug going from good->bad->same good expression.

Because the final transition doesn't actually cause the expression to change, we can't rely on __update() to hide the error panel for us, so we just do it directly.

hradec/gaffer,boberfly/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,chippey/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,chippey/gaffer,appleseedhq/gaffer,boberfly/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,hradec/gaffer,boberfly/gaffer,ivanimanishi/gaffer,chippey/gaffer,GafferHQ/gaffer,hradec/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,chippey/gaffer,ImageEngine/gaffer,appleseedhq/gaffer,hradec/gaffer,boberfly/gaffer,GafferHQ/gaffer,ivanimanishi/gaffer,hradec/gaffer,ImageEngine/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer