Blueprint functions with unconnected return nodes may return unexpected values

We don't clearly define the behavior for a Blueprint function when an execution path without a return node is taken. We should either report an error, or have the function return the default initialization of the type (eg: false for bool, 0 for int, etc).

• Download WDT_Test.uasset attachment.
• Create an empty map.
• Open the level Blueprint.
• Add a "Create Widget" node to the BeginPlay event.
• Set WDT_Test as the widget class for the node.
• Connect a GetPlayerController node to the Owning Player pin of the widget node.
• Connect a Add to Viewport node to the widget node's output.
• In WDT_Test's TestFunc, set a breakpoint on the print node that displays "Func: False".
• Play in viewport.
• After breakpoint hits, step out of function.
• Observe that the branch in the even graph takes the true path and not that false one.