Check if ctx or model is null before calling sampler

[gagankonana]

Add a check in main in completion.cpp to check if ctx or model is null before calling sampler. This validates that common_init_from_params was successful
Resolves #19065

[ggerganov]

This seems to hide some other problem - it's not a valid solution

[danbev]

This seems to hide some other problem - it's not a valid solution

Ah yes, it looks like this is because the model is failing to load but we are calling llama_init->sampler(0) without checking the context here:

llama.cpp/tools/completion/completion.cpp

Lines 144 to 146 in 56f3ebf

	ctx = llama_init->context();
	model = llama_init->model();
	smpl = llama_init->sampler(0);

We should move check of the ctx before this call.

[gagankonana]

Updated the PR. I followed the pattern from other files. Let me know wdyt

[danbev]

Updated the PR. I followed the pattern from other files. Let me know wdyt

Thanks! This looks good to me. Can you also take a look at the EditorConfig Checker CI failure?