Really fix top of fullscreen window being cut off in GNOME

See 4df6e5c

src/sdl/window.cpp

@@ -98,6 +98,9 @@ Window::Window(const std::string& title, int width, int height, const bool fulls
 		}
 	}
 
+#ifndef __linux__ // This code was written for UWP, Emscripten and macOS (annoying HiDPI scaling by
+                  // SDL2). On Linux (GNOME) it results in the top of the window being cut off (by
+                  // the header bar height?).
 	{
 		assert(width_ == width);
 		assert(height_ == height);
@@ -122,6 +125,7 @@ Window::Window(const std::string& title, int width, int height, const bool fulls
 	}
 
 	SDL_GL_GetDrawableSize(impl->sdlWindow, &width_, &height_);
+#endif
 	impl->actualWidth = width_;
 	impl->actualHeight = height_;
 	impl->hidpiScaleFactor = static_cast<float>(width_) / width;