common : throw instead of abort on grammar without llguidance (#29516)

Signed-off-by: Adrien Gallouët <[email protected]>

common/sampling.cpp

@@ -214,7 +214,7 @@ struct common_sampler * common_sampler_init(
 #ifdef LLAMA_USE_LLGUIDANCE
         grmr = llama_sampler_init_llg(vocab, "lark", grammar_str.c_str());
 #else
-        GGML_ABORT("llguidance (cmake -DLLAMA_LLGUIDANCE=ON) is not enabled");
+        throw std::runtime_error("failed to parse grammar: llguidance is not enabled");
 #endif // LLAMA_USE_LLGUIDANCE
     } else {
         std::vector<std::string> trigger_patterns;