Instead of juggling with this problem during literal compaction,
make sure that we always initialize Z_EXTRA for literals, which
seems like the more robust solution.

Remove invalid assertion: A block can have multiple switch frees,
so if we don't do live range block splitting, it is not necessarily
true that the free is located at the start of a block.

Signed-off-by: Elan Ruusamäe <glen@pld-linux.org>

Weird that this worked for so long, probably because nearly all
ext/standard functions use fast ZPP rather than ordinary ZPP.

This was respected only for the single-function optimizations, not
in func-info mode.