remove unnecessary test of ViewPager position, since the callback will only be enabled if the position is not 0.

app/src/main/java/com/keylesspalace/tusky/MainActivity.kt

@@ -196,9 +196,7 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidInje
 
     private val onBackPressedCallback = object : OnBackPressedCallback(false) {
         override fun handleOnBackPressed() {
-            if (binding.viewPager.currentItem != 0) {
-                binding.viewPager.currentItem = 0
-            }
+            binding.viewPager.currentItem = 0
         }
     }