tools : fix invalid free()

[aumfer]

Added a constructor to server_context that initializes server_context::batch, preventing the destructor's call to llama_batch_free() from causing an invalid free().

Ran into this when bind() failed.

[aumfer]

There are other ways to solve this if you don't want to zero out the entire llama_batch object. (eg track whether server_context::init() has been called, check in the destructor before calling llama_batch_free)

[ngxson]

I think the proper fix is to check if batch.embd is not nullptr before freeing it. This is the same pattern with other _free functions in llama.cpp where we do nothing given a nullptr

[slaren]

Both free and delete will ignore a null pointer, these checks are not necessary. The problem here is uninitialized memory.

[ngxson]

Ok that makes sense. I think this can be the temporary solution before we finally have the private batch API.