Partially fix data race issues around _cur_palette

See: https://github.com/OpenTTD/OpenTTD/issues/8712

src/video/sdl2_opengl_v.cpp

@@ -141,6 +141,7 @@ bool VideoDriver_SDL_OpenGL::AllocateBackingStore(int w, int h, bool force)
 	_cur_palette.first_dirty = 0;
 	_cur_palette.count_dirty = 256;
 	this->local_palette = _cur_palette;
+	_cur_palette.count_dirty = 0;
 
 	return res;
 }
@@ -165,7 +166,7 @@ void VideoDriver_SDL_OpenGL::Paint()
 {
 	PerformanceMeasurer framerate(PFE_VIDEO);
 
-	if (_cur_palette.count_dirty != 0) {
+	if (this->local_palette.count_dirty != 0) {
 		Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
 		/* Always push a changed palette to OpenGL. */
@@ -174,7 +175,7 @@ void VideoDriver_SDL_OpenGL::Paint()
 			blitter->PaletteAnimate(this->local_palette);
 		}
 
-		_cur_palette.count_dirty = 0;
+		this->local_palette.count_dirty = 0;
 	}
 
 	OpenGLBackend::Get()->Paint();

src/video/win32_v.cpp

@@ -887,6 +887,7 @@ void VideoDriver_Win32Base::ClientSizeChanged(int w, int h, bool force)
 		_cur_palette.first_dirty = 0;
 		_cur_palette.count_dirty = 256;
 		_local_palette = _cur_palette;
+		_cur_palette.count_dirty = 0;
 
 		BlitterFactory::GetCurrentBlitter()->PostResize();
 
@@ -1136,7 +1137,7 @@ void VideoDriver_Win32GDI::Paint()
 	HBITMAP old_bmp = (HBITMAP)SelectObject(dc2, this->dib_sect);
 	HPALETTE old_palette = SelectPalette(dc, this->gdi_palette, FALSE);
 
-	if (_cur_palette.count_dirty != 0) {
+	if (_local_palette.count_dirty != 0) {
 		Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
 		switch (blitter->UsePaletteAnimation()) {
@@ -1155,7 +1156,7 @@ void VideoDriver_Win32GDI::Paint()
 			default:
 				NOT_REACHED();
 		}
-		_cur_palette.count_dirty = 0;
+		_local_palette.count_dirty = 0;
 	}
 
 	BitBlt(dc, 0, 0, this->width, this->height, dc2, 0, 0, SRCCOPY);
@@ -1447,7 +1448,7 @@ void VideoDriver_Win32OpenGL::Paint()
 {
 	PerformanceMeasurer framerate(PFE_VIDEO);
 
-	if (_cur_palette.count_dirty != 0) {
+	if (_local_palette.count_dirty != 0) {
 		Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
 		/* Always push a changed palette to OpenGL. */
@@ -1456,7 +1457,7 @@ void VideoDriver_Win32OpenGL::Paint()
 			blitter->PaletteAnimate(_local_palette);
 		}
 
-		_cur_palette.count_dirty = 0;
+		_local_palette.count_dirty = 0;
 	}
 
 	OpenGLBackend::Get()->Paint();