Crash: LyftButton#displayCost referring to CostEstimate#estimated_cost_cents_min which is null starting Aug 25, 2021

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We're getting a crash in the SeatGeek app due to the LyftButton failing to set the cost on the button as a result its API request for cost estimates, with this field (and presumably others it can't reach) being null or omitted from the response.

Stack trace:
```
Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Integer.intValue()' on a null object reference
at com.lyft.lyftbutton.LyftButton.displayCost(LyftButton.java:191)
at com.lyft.lyftbutton.LyftButton.access$300(LyftButton.java:21)
at com.lyft.lyftbutton.LyftButton$2.onSuccess(LyftButton.java:160)
at com.lyft.lyftbutton.LyftButtonCallManager$4.onResponse(LyftButtonCallManager.java:184)
at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1.lambda$onResponse$0(DefaultCallAdapterFactory.java:89)
at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1.lambda$onResponse$0$DefaultCallAdapterFactory$ExecutorCallbackCall$1(DefaultCallAdapterFactory.java:3)
at retrofit2.-$$Lambda$DefaultCallAdapterFactory$ExecutorCallbackCall$1$hVGjmafRi6VitDIrPNdoFizVAdk.run(-.java:3)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8595)
```

Start at LyftButton.java:191, where displayCost crashes while processing the CostEstimate response, and inspect the response handling around LyftButtonCallManager.java:184. Reproduce or trace the null estimated_cost_cents_min case and review how other possibly omitted fields are handled. Done means a response with null or omitted cost fields no longer crashes the button.

Written by the indexing model from the issue text.