Fix Snackbar not dismissing bug

When Snackbar was displayed while another Snackbar was displayed,
the last ref to the current Snackbar was removed and it didn't get removed
when onScreenChange was called.

android/app/src/main/java/com/reactnativenavigation/views/SnackbarAndFabContainer.java

@@ -36,8 +36,10 @@ public class SnackbarAndFabContainer extends CoordinatorLayout implements Snakba
     }
 
     @Override
-    public void onDismiss() {
-        snakbar = null;
+    public void onDismiss(Snakbar snakbar) {
+        if (this.snakbar == snakbar) {
+            this.snakbar = null;
+        }
     }
 
     public void destroy() {

android/app/src/main/java/com/reactnativenavigation/views/Snakbar.java

@@ -13,7 +13,7 @@ public class Snakbar {
     private Snackbar snackbar;
 
     public interface OnDismissListener {
-        void onDismiss();
+        void onDismiss(Snakbar snakbar);
     }
 
     public void show() {
@@ -68,7 +68,7 @@ public class Snakbar {
 
             @Override
             public void onViewDetachedFromWindow(View v) {
-                parent.onDismiss();
+                parent.onDismiss(Snakbar.this);
             }
         });
     }