MemoryBuffer: Handle empty memory objects properly
MemoryBuffer: Handle empty memory objects properly

Signed-off-by: Dmitry Fleytman <f50f56ffad4b379c2a89812e98b14900ef87e9ea@redhat.com>

daynix/UsbDk,SPICE/win32-usbdk,SPICE/win32-usbdk,daynix/UsbDk