Avoid placing precompleted rewards on Rauru

[fenhl]

Fixes a bug where, when “Pre-completed Dungeons Mode” is set to “Specific Rewards”, the randomizer could place one of the specified rewards on the ToT Reward from Rauru location, resulting in one fewer precompleted dungeon than expected.

This fix is conceptually similar to an existing feature where in “Count” mode, non-MQ dungeons are prioritized to be selected as precompleted before MQ dungeons.

Testing

Tested using ootrstats with a settings string that has the Kokiri Emerald and Goron Ruby precompleted:

• ootrstats --settings=BSAWDNCAX2TB2XCHGABSL62ANAEACASSSACAASBEASHASFAAJAJUJJASCACC6AJXAQL6KT2LAASAGADWBRAJCEH7KYCAF3WQYAAAJLNBA3CGZA2SRES8WBTPAZCAEGJNQ6A6B6DJAJTA3JGE categorize '.locations["ToT Reward from Rauru"]' reported that Rauru had the Kokiri Emerald in 1779 and the Goron Ruby in 1831 out of 16384 seeds, with 1 generator failure.
• ootrstats -ufenhl -bprecompleted-rauru --settings=BSAWDNCAX2TB2XCHGABSL62ANAEACASSSACAASBEASHASFAAJAJUJJASCACC6AJXAQL6KT2LAASAGADWBRAJCEH7KYCAF3WQYAAAJLNBA3CGZA2SRES8WBTPAZCAEGJNQ6A6B6DJAJTA3JGE categorize '.locations["ToT Reward from Rauru"]' reported no instances of Rauru holding either reward, with 0 generator failures.

[fenhl]

For the record and since the concern was brought up on Discord, the stats run showed that the numbers for the other rewards were fairly similar to each other, i.e. rewards were still properly shuffled.