kleidiai: fix unsigned overflow bug (ggml-org#15150)

* kleidiai: fix unsigned overflow bug

* address review comments

Author: chaxu01

ggml/src/ggml-cpu/kleidiai/kleidiai.cpp

@@ -259,7 +259,10 @@ class tensor_traits : public ggml::cpu::tensor_traits {
                 const int64_t m_start      = 0;
 
                 const int64_t n_step      = static_cast<int64_t>(kernel->get_n_step());
-                const int64_t num_threads = KAI_MIN(n / n_step, nth);
+                int64_t num_threads       = KAI_MIN(n / n_step, nth);
+                if (num_threads <= 0) {
+                    num_threads = 1;
+                }
 
                 if (ith < num_threads) {
                     const int64_t num_n_per_thread0   = round_down(n / num_threads, n_step);
@@ -309,7 +312,8 @@ class tensor_traits : public ggml::cpu::tensor_traits {
         GGML_ASSERT(kernel);
 
         const int ith = params->ith;
-        const int nth = params->nth;
+        const int nth_raw = params->nth;
+        const int nth = nth_raw > 0 ? nth_raw : 1;
 
         const size_t k = ne00;
         const size_t m = ne11;
@@ -327,9 +331,12 @@ class tensor_traits : public ggml::cpu::tensor_traits {
         const size_t num_n_per_thread = kai_roundup(kai_roundup(n, nth) / nth, n_step);
         const size_t n_start = ith * num_n_per_thread;
 
-        size_t n_to_process = num_n_per_thread;
-        if ((n_start + n_to_process) > n) {
-            n_to_process = n - n_start;
+        size_t n_to_process = 0;
+        if (n_start < n) {
+            n_to_process = num_n_per_thread;
+            if ((n_start + n_to_process) > n) {
+                n_to_process = n - n_start;
+            }
         }
 
         // Calculate number of columns to be processed per thread
@@ -361,8 +368,10 @@ class tensor_traits : public ggml::cpu::tensor_traits {
         const void* lhs_ptr            = (const void*)((const char *)lhs_packed + lhs_packed_offset);
         float *dst_ptr                 = reinterpret_cast<float *>(static_cast<uint8_t *>(dst->data) + dst_offset);
 
-        variant_call<void>(kernel->run_kernel, m, n_to_process, k, QK4_0, lhs_ptr, rhs_ptr, dst_ptr, dst_stride,
-                           sizeof(float), -FLT_MAX, FLT_MAX);
+        if (n_to_process > 0) {
+            variant_call<void>(kernel->run_kernel, m, n_to_process, k, QK4_0, lhs_ptr, rhs_ptr, dst_ptr, dst_stride,
+                               sizeof(float), -FLT_MAX, FLT_MAX);
+        }
 
         return true;
     }