d3d: Make sure vertexbuffer lock doesn't return a NULL pointer.

dlls/d3d8/tests/buffer.c

@@ -104,6 +104,7 @@ static void lock_flag_test(IDirect3DDevice8 *device)
 
         if(SUCCEEDED(hr))
         {
+            ok(data != NULL, "The data pointer returned by Lock is NULL\n");
             hr = IDirect3DVertexBuffer8_Unlock(buffer);
             ok(hr == D3D_OK, "IDirect3DVertexBuffer8_Unlock failed, 0x%08x\n", hr);
         }

dlls/d3d9/tests/buffer.c

@@ -103,6 +103,7 @@ static void lock_flag_test(IDirect3DDevice9 *device)
 
         if(SUCCEEDED(hr))
         {
+            ok(data != NULL, "The data pointer returned by Lock is NULL\n");
             hr = IDirect3DVertexBuffer9_Unlock(buffer);
             ok(hr == D3D_OK, "IDirect3DVertexBuffer9_Unlock failed, 0x%08x\n", hr);
         }

dlls/ddraw/tests/d3d.c

@@ -3216,6 +3216,7 @@ static void VertexBufferLockRest(void)
             test_data[i].debug_string, hr, test_data[i].result);
         if(SUCCEEDED(hr))
         {
+            ok(data != NULL, "The data pointer returned by Lock is NULL\n");
             hr = IDirect3DVertexBuffer7_Unlock(buffer);
             ok(hr == D3D_OK, "IDirect3DVertexBuffer7_Unlock failed, 0x%08x\n", hr);
         }