Investigate code in SViewport.cpp that makes use of TWeakPtr's to see if it can be altered to better protect against a possible crash.

A user reported a one-time crash that possibly occurred when a TWeakPtr became invalid immediately after passing an IsValid check, before the TWeakPtr could be used. The SViewport.cpp file contains several instances of code that uses the following pattern:

if (ViewportInterface.IsValid())
     {
         ViewportInterface.Pin()->OnMouseLeave(MouseEvent);
     }

The user suggested that this code may be better written as follows:

TSharedPtr<ISlateViewport> PinnedInterface = ViewportInterface.Pin();
if (PinnedInterface.IsValid())
     {
         PinnedInterface->OnMouseLeave(MouseEvent);
     }

Please investigate whether using Pin prior to IsValid in these cases would be better able to prevent a potential race condition.

Note: I was unable to repro the actual crash that the user experienced, and they apparently only saw it happen a single time.

1. Open the UE4.sln file in Visual Studio.
2. Open the SViewport.cpp file.
3. Locate the SViewport::OnMouseLeave function.

RESULT:
The code in the first code snippet shown in the Description is visible.

EXPECTED:
The code in the second code snippet shown in the Description may be safer.