Fix polymer 2 bug in app-media-image-capture

[j0000el]

In polymer 2, observed properties can be undefined, so properly handle those cases. Fixes bug where "Failed to construct 'ImageCapture'" exception is thrown causing subsequent calls to takePhoto() to fail.

Fixes #59

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[e111077]

Nice, please resolve the CLA issue and this PR is good to go!

[e111077]

Closing. Please reopen when CLA issue is resolved. Thanks!

[j0000el]

I signed it!

[e111077]

Can you try to kick it one more time? If not, I'd check your commit history to see if it was authored with the correct email address.

[j0000el]

Created #61 with the correct email address.