[REG2.065a] Issue 11925 - ICE in CompoundStatement::semantic

https://d.puremagic.com/issues/show_bug.cgi?id=11925

@ibuclaw As far as I know, `void insert(size_t index, Array *a)` should work even if `a->dim == 0`. The root issue exists in `CompoundStatement::semantic`. That's the case I had overlooked.