Screen share not working if pixman does not provide pixman_blt

In case pixman has been compiled without any accelerated blitting function, pixman_blt will return false. In this case copying the pixel data will not occurs and the shared screen remains black.

I noticed this on Weston 6.0.0 compiled for Arm aarch64 with latest pixman (0.38.4). Currently pixman does not provide a implementation for pixman_blt when compiling for aarch64. In that case the shared screen (via RDP in my case) remained black on the remote end.

According to @siamashka a user of pixman_blt should expect that pixman_blt returns false and implement a fallback mechanism in this case. See also this mailing list discussion: https://lists.freedesktop.org/archives/pixman/2013-December/003135.html