ENYO-382: Access the correct source/target properties.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
ENYO-382: Ensure the binding property (source/target) actually exists before accessing its properties.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
Merge pull request #912 from enyojs/ENYO-382-aarontam

ENYO-382: Access the correct source/target properties.

Reviewed-By: Ryan Duffy (ryan.duffy@lge.com)
Integrated-By: Cole Davis (cole.davis@lge.com)