fix(android): race condition on offBackgroundColor view change detection

[NathanWalker]

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What is the current behavior?

Various framework integrations, like Angular, may invoke view change detection cycles on property bindings at times when the nativeView is not available resulting in errors like:

JS: ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'getTrackDrawable' of undefined
JS: TypeError: Cannot read property 'getTrackDrawable' of undefined
JS:     at Switch.setNativeBackgroundColor (file: src/webpack:/app/node_modules/@nativescript/core/ui/switch/index.android.js:48:0)
JS:     at Switch._onCheckedPropertyChanged (file: src/webpack:/app/node_modules/@nativescript/core/ui/switch/index.android.js:61:0)

What is the new behavior?

Switch is now resilient to this.

[farfromrefug]

@NathanWalker shouldn't this be handle on the property side ? isn't it already? don't think we want this test everywhere. the property setter handler seems like a better place to me

[NathanWalker]

@farfromrefug good question, it seems that because this function is reused several places, it's called outside the Property mechanics at times leading to the issue.