core: fix reload interval parsing (#4584)
core: fix reload interval parsing (#4584)

Summary:
Fixes an error in #4583. Not sure how this slipped my testing; perhaps
I committed incorrectly.

Test Plan:
Follow the test plan from #4583, and double-check that data actually
loads in the UI.

wchargin-branch: fix-reload-interval

tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard