Fabric: Do not crash in attempt to mount layout-only components

Summary: We do not have a clear strategy how to deal with layout-only (view-less) components. Even if this particular solution is not so fancy, it prevents crashing during text rendering.

Reviewed By: mdvacca

Differential Revision: D7785885

fbshipit-source-id: f3ed8988aa2b41349fd1693c2a7f8c9368daee43

React/Fabric/Mounting/MountItems/RCTDeleteMountItem.mm

@@ -28,6 +28,11 @@
 - (void)executeWithRegistry:(RCTComponentViewRegistry *)registry
 {
   UIView<RCTComponentViewProtocol> *componentView = [registry componentViewByTag:_tag];
+
+  if (componentView == nil) {
+    return;
+  }
+
   [registry enqueueComponentViewWithName:_componentName tag:_tag componentView:componentView];
 }
 

React/Fabric/Mounting/MountItems/RCTInsertMountItem.mm

@@ -33,6 +33,10 @@
   UIView<RCTComponentViewProtocol> *childComponentView = [registry componentViewByTag:_childTag];
   UIView<RCTComponentViewProtocol> *parentComponentView = [registry componentViewByTag:_parentTag];
 
+  if (childComponentView == nil || parentComponentView == nil) {
+    return;
+  }
+
   [parentComponentView mountChildComponentView:childComponentView
                                          index:_index];
 }

React/Fabric/Mounting/MountItems/RCTRemoveMountItem.mm

@@ -33,6 +33,10 @@
   UIView<RCTComponentViewProtocol> *childComponentView = [registry componentViewByTag:_childTag];
   UIView<RCTComponentViewProtocol> *parentComponentView = [registry componentViewByTag:_parentTag];
 
+  if (childComponentView == nil || parentComponentView == nil) {
+    return;
+  }
+
   [parentComponentView unmountChildComponentView:childComponentView
                                            index:_index];
 }