remove deprecated call to isUserVisibleHint() and test if the view has been destroyed instead.

prevent potential memory leak by clearing the toolbarVisibilityDisposable reference.

app/src/main/java/com/keylesspalace/tusky/fragment/ViewImageFragment.kt

@@ -45,9 +45,9 @@ import com.keylesspalace.tusky.util.viewBinding
 import com.keylesspalace.tusky.util.visible
 import com.ortiz.touchview.OnTouchCoordinatesListener
 import com.ortiz.touchview.TouchImageView
-import kotlin.math.abs
 import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.launch
+import kotlin.math.abs
 
 class ViewImageFragment : ViewMediaFragment() {
     interface PhotoActionsListener {
@@ -232,7 +232,7 @@ class ViewImageFragment : ViewMediaFragment() {
     }
 
     override fun onToolbarVisibilityChange(visible: Boolean) {
-        if (!userVisibleHint) return
+        if (view == null) return
 
         isDescriptionVisible = showingDescription && visible
         val alpha = if (isDescriptionVisible) 1.0f else 0.0f

app/src/main/java/com/keylesspalace/tusky/fragment/ViewMediaFragment.kt

@@ -100,6 +100,7 @@ abstract class ViewMediaFragment : Fragment() {
 
     override fun onDestroyView() {
         toolbarVisibilityDisposable?.invoke()
+        toolbarVisibilityDisposable = null
         super.onDestroyView()
     }
 }

app/src/main/java/com/keylesspalace/tusky/fragment/ViewVideoFragment.kt

@@ -379,7 +379,7 @@ class ViewVideoFragment : ViewMediaFragment(), Injectable {
     }
 
     override fun onToolbarVisibilityChange(visible: Boolean) {
-        if (!userVisibleHint) {
+        if (view == null) {
             return
         }