Random Stream variables in the GameMode are reset every PIE

Random Stream variables in the GameMode are reset every PIE.

Workaround is to use Set Random Stream Seed before using the Stream value.

Reproduced in 4.7.6, 4.8.1, and Main (//depot/UE4/Promotable-CL-2610743)

1. Open any project
2. Create a new GameMode Blueprint
3. Set the GameMode as default for the project or level
4. Create a Random Stream variable
5. On Event Begin Play, Random Stream variable > Break Random Stream > Print String
6. Compile / Save
7. PIE
8. Stop
9. PIE

Result:
The number printed resets on replaying

Expected:
The number printed maintains the same value every replay, as it would in an instance of an Actor Blueprint in the level