fix: Empty array & null checks in handleTabNavigatorChange method fixes

#6698 (#6700)

Fixes:  Shared Element Transition (Solution provided) #6698 

Add safety checks in handleTabNavigatorChange to prevent crash

This fixes a crash that occurs when _disappearingScreens array is empty
or
contains invalid objects by adding appropriate null checks and bounds
checking.

The crash would occur when:
- The _disappearingScreens array is empty
- navTabScreen or its reactSuperview is null
- targetScreen is null

App was crashing during shared element transition because of invalid
array access.

Fixes #6698

---------

Co-authored-by: Krzysztof Piaskowy <krzysztof.piaskowy@swmansion.com>

packages/react-native-reanimated/apple/reanimated/apple/LayoutReanimation/REASharedTransitionManager.m

@@ -576,10 +576,26 @@ - (void)handleTabNavigatorChange:(REAUIView *)layoutedScreen
     return;
   }
 
+  // Add safety check for disappearing screens
+  if ([_disappearingScreens count] == 0) {
+    return;
+  }
+
   REAUIView *navTabScreen = _disappearingScreens[0];
   REAUIView *sourceScreen = _disappearingScreens[[_disappearingScreens count] - 1];
+
+  // Add null checks
+  if (!navTabScreen || !navTabScreen.reactSuperview) {
+    return;
+  }
+
   REAUIView *targetTabScreen = [REAScreensHelper getActiveTabForTabNavigator:navTabScreen.reactSuperview];
   REAUIView *targetScreen = [REAScreensHelper findTopScreenInChildren:targetTabScreen];
+
+  if (!targetScreen) {
+    return;
+  }
+
   if (!layoutedScreen && _isTabNavigator) {
     // just wait for the next layout computation for your screen
     return;