BHV-15858: Explicitly show slider knob when slider is re-enabled.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
Merge pull request #1711 from enyojs/BHV-15858-aarontam

BHV-15858: Explicitly show slider knob when slider is re-enabled.

Reviewed-By: Art Dahm (art.dahm@lge.com)
Integrated-By: Cole Davis (cole.davis@lge.com)