avoid crashes in rare case when tabParent is not initialized

```
Exception b5.e: lateinit property tabParent has not been initialized
  at app.grapheneos.camera.ui.BottomTabLayout.centerTab (BottomTabLayout.kt)
  at app.grapheneos.camera.ui.activities.MainActivity.finalizeMode (MainActivity.kt)
```

Author: empratyush

app/src/main/java/app/grapheneos/camera/ui/BottomTabLayout.kt

@@ -94,6 +94,7 @@ class BottomTabLayout @JvmOverloads constructor(
     }
 
     fun centerTab(tab: Tab) {
+        if (!this::tabParent.isInitialized) return
         val targetScrollX = calculateScrollXForTab(tab.position)
 
         if (scrollX != targetScrollX)