Merge pull request #718 from jmfergeau/patch-1

fix:  Jukebox graphics not displaying correctly

src/base/UImage.pas

@@ -734,6 +734,7 @@ procedure ColorizeImage(ImgSurface: PSDL_Surface; NewColor: longword);
       //       PixelColors[3] is alpha and remains untouched
       Inc(Pixel, ImgSurface^.format.BytesPerPixel);
     end;
+    SDL_UnlockSurface(ImgSurface);
     exit; // we are done with a greyscale image.
   end;