Fix fishing trawler issue

What has been done in this MR?

• Make fishing trawler calculate its number of reward rolls during the game session, storing just this result instead of storing a reference to the entire game session. Fixes #1912 as well as loot getting lost when you log after having won.
• Dammit gitlab, I said FIXES #1912

What should testers check?

• You get loot when you expect it and you don't when you don't
• Leaving the boat before the game starts does not get you sucked into the game anyway
• ::rolltrawlerloot did not get broken

• I have tested these changes thoroughly.

• I used the relevant Zaros tool for any JSON edits where possible, and have attached screenshots of any changes.