Warn if pixman_blt fails in screen share
pixman_blt fails we silently ignore this. Typically
pixman_blt fails if there is no accelerated version of it available. It seems that
pixman_blt expects the user to fall back to a local implementation in case pixman has no accelerated version available. Warn in this case so the user has at least a hint what went wrong.
References #253 (closed)