PixelPaint: Avoid unnecessary temporary layer bitmaps during PP load

When opening a PP file, we were creating a layer first with an empty
bitmap, and then replacing it with the loaded bitmap from the file.

This patch reorders things so we never create the empty bitmap in
between, saving time and avoiding a memory spike.

Userland/Applications/PixelPaint/Image.cpp

@@ -104,25 +104,30 @@ Result<NonnullRefPtr<Image>, String> Image::try_create_from_pixel_paint_file(Str
     auto layers_value = json.get("layers");
     for (auto& layer_value : layers_value.as_array().values()) {
         auto& layer_object = layer_value.as_object();
-        auto width = layer_object.get("width").to_i32();
-        auto height = layer_object.get("height").to_i32();
         auto name = layer_object.get("name").as_string();
-        // FIXME: Delay Layer creation until we have the bitmap, to avoid an unnecessary temporary bitmap here!
-        auto layer = Layer::try_create_with_size(*image, { width, height }, name);
-        if (!layer)
-            return String { "Layer memory allocation failed" };
-        layer->set_location({ layer_object.get("locationx").to_i32(), layer_object.get("locationy").to_i32() });
-        layer->set_opacity_percent(layer_object.get("opacity_percent").to_i32());
-        layer->set_visible(layer_object.get("visible").as_bool());
-        layer->set_selected(layer_object.get("selected").as_bool());
 
         auto bitmap_base64_encoded = layer_object.get("bitmap").as_string();
         auto bitmap_data = decode_base64(bitmap_base64_encoded);
 
         auto bitmap = try_decode_bitmap(bitmap_data);
         if (!bitmap)
-            return String { "Layer bitmap decode failed" };
-        layer->set_bitmap(bitmap.release_nonnull());
+            return String { "Layer bitmap decode failed"sv };
+
+        auto layer = Layer::try_create_with_bitmap(*image, bitmap.release_nonnull(), name);
+        if (!layer)
+            return String { "Layer allocation failed"sv };
+
+        auto width = layer_object.get("width").to_i32();
+        auto height = layer_object.get("height").to_i32();
+
+        if (width != layer->size().width() || height != layer->size().height())
+            return String { "Decoded layer bitmap has wrong size"sv };
+
+        layer->set_location({ layer_object.get("locationx").to_i32(), layer_object.get("locationy").to_i32() });
+        layer->set_opacity_percent(layer_object.get("opacity_percent").to_i32());
+        layer->set_visible(layer_object.get("visible").as_bool());
+        layer->set_selected(layer_object.get("selected").as_bool());
+
         image->add_layer(*layer);
     }