Using a memcpy here is supremely dangerous, because we are writing to
an app_server buffer that we chose the length for, but using a size
that came from the client. And, indeed, because the buffer can contain
padding if the BBitmap was allocated with a non-standard BytesPerRow,
we will overflow the buffer and corrupt memory, causing app_server to crash.
So, instead, reorganize parameters a bit, and pass BytesPerRow along
with the other data needed to instantiate the bitmap, and then use
ImportBits.
Fixes an app_server crash I triggered with the experimental libX11
compatibility layer.
0cdb323800