image: do not alter the pointer returned by Lock().

src/image/codec/dummy-image.cpp

@@ -40,15 +40,15 @@ bool DummyImageCodec::Load(Image *image, char const *path)
     UNUSED(path);
 
     image->SetSize(ivec2(256));
-    u8vec4 *pixels = image->Lock<PixelFormat::RGBA_8>();
+    u8vec4 *pixels = image->Lock<PixelFormat::RGBA_8>(), *tmp = pixels;
     for (int j = 0; j < 256; j++)
         for (int i = 0; i < 256; i++)
         {
-            pixels->r = ((i ^ j) & 1) * 0xff;
-            pixels->g = (uint8_t)i;
-            pixels->b = (uint8_t)j;
-            pixels->a = (((i >> 4) ^ (j >> 4)) & 1) * 0xff;
-            ++pixels;
+            tmp->r = ((i ^ j) & 1) * 0xff;
+            tmp->g = (uint8_t)i;
+            tmp->b = (uint8_t)j;
+            tmp->a = (((i >> 4) ^ (j >> 4)) & 1) * 0xff;
+            ++tmp;
         }
     image->Unlock(pixels);