Fix blocknode iterating and simplify P_BlockThingsIterator

Fixes #1323 (closed). Don't ask me how I found that out.

Additionally, this reverts P_BlockThingsIterator to how it was before 7469a627, but holds the reference properly.

added Optimisation label

added 7 commits

• c9a1984d...e570328c - 6 commits from branch next
• fcb4948e - Merge branch 'next' into simplify-blockthingsiterator

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added 1 commit

• ebc29ef0 - Fix more code that uses block->mnext

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changed title from Simplify P_BlockThingsIterator to Simplify P_BlockThingsIterator and fix blocknode iterating

changed the description

changed milestone to %2.2.14

changed title from Simplify P_BlockThingsIterator and fix blocknode iterating to Fix blocknode iterating and simplify P_BlockThingsIterator

changed the description

merged

mentioned in commit 292b735d