Halt stack.h with an error if multi-memories are present

[ashleynh]

This pass can probably halt with an error (like on line 49 above) if there are no memories. Please also add a comment that we are assuming that memory 0 is the "main" memory here.

Originally posted by @kripken in https://github.com/WebAssembly/binaryen/pull/4811#discussion_r933611134