fix: Nullable build errors on iOS

Author: MartinZikmund

src/Uno.UWP/Storage/StorageFile.iOS.cs

@@ -89,7 +89,8 @@ public override async Task<Stream> OpenStreamAsync(CancellationToken ct, FileAcc
 			public override Task<StorageStreamTransaction> OpenTransactedWriteAsync(CancellationToken ct, StorageOpenOptions option) => throw new NotImplementedException();
 
 			protected override bool IsEqual(ImplementationBase implementation) =>
-				implementation is SecurityScopedFile file && file._nsUrl.FilePathUrl.Path == _nsUrl.FilePathUrl.Path;
+				implementation is SecurityScopedFile file && 
+				file._nsUrl.FilePathUrl?.Path == _nsUrl.FilePathUrl?.Path;
 		}
 	}
 }

src/Uno.UWP/Storage/StorageFolder.iOS.cs

@@ -299,7 +299,8 @@ public override Task<IReadOnlyList<IStorageItem>> GetItemsAsync(CancellationToke
 			}
 
 			protected override bool IsEqual(ImplementationBase implementation) =>
-				implementation is SecurityScopedFolder otherFolder && otherFolder._nsUrl.FilePathUrl.Path == _nsUrl.FilePathUrl.Path;
+				implementation is SecurityScopedFolder otherFolder && 
+				otherFolder._nsUrl.FilePathUrl?.Path == _nsUrl.FilePathUrl?.Path;
 		}
 	}
 }