llama : check returned fn ptrs from ggml_backend_reg_get_proc_address (#15893)

This commit adds check for two function pointers returned from
ggml_backend_reg_get_proc_address.

The motivation for this is that the function pointer could be nullptr if
the get proc address function changes in the future. This is also
consistent with all the other calls to ggml_backend_reg_get_proc_address
in the code base.

src/llama-context.cpp

@@ -1447,7 +1447,9 @@ ggml_status llama_context::graph_compute(
     if (backend_cpu != nullptr) {
         auto * reg = ggml_backend_dev_backend_reg(ggml_backend_get_device(backend_cpu));
         auto * set_threadpool_fn = (decltype(ggml_backend_cpu_set_threadpool) *) ggml_backend_reg_get_proc_address(reg, "ggml_backend_cpu_set_threadpool");
-        set_threadpool_fn(backend_cpu, tp);
+        if (set_threadpool_fn) {
+            set_threadpool_fn(backend_cpu, tp);
+        }
     }
 
     // set the number of threads for all the backends

src/llama.cpp

@@ -83,7 +83,9 @@ void llama_numa_init(enum ggml_numa_strategy numa) {
         GGML_ASSERT(dev && "CPU backend is not loaded");
         auto * reg = ggml_backend_dev_backend_reg(dev);
         auto * numa_init_fn = (decltype(ggml_numa_init) *) ggml_backend_reg_get_proc_address(reg, "ggml_backend_cpu_numa_init");
-        numa_init_fn(numa);
+        if (numa_init_fn) {
+            numa_init_fn(numa);
+        }
     }
 }