Summary:
If you have a measurable node and set ```marign-left: auto``` + ```align-item:stretch``` on it, it won't get measured and they get a width/height of ```-(nan)```. This change fixes that behaviour. Fixes#644.
Closes https://github.com/facebook/yoga/pull/645
Differential Revision: D6413512
Pulled By: emilsjolander
fbshipit-source-id: 755febeb33bb0d4520ca6b3c28d56ac333e4a14d