Fix if propagation

[danog]

Fixes #8317

[danog]

This reverts what is essentially a simplification of if handling logic, since the old logic allowed for patterns that aren't that uncommon in real code (an example is included in a new testcase).

[orklah]

@muglug could you take a look at #8317 please? Maybe there's an easier fix rather than reverting the whole thing?

[muglug]

Looks good! At some point I might try to figure out a solution that works with else if, and the nested of example I gave, but for now I’m happy to revert my change.