VGDrvCommonIoCtl may be potentially dereferencing a null pointer on pcbDataReturned

[ColinIanKing]

Function VGDrvCommonIoCtl in src/VBox/Additions/common/VBoxGuest/VBoxGuest.cpp is checking to see if pcbDataReturned is NULL and then setting it to zero, thus the code assumes there is a potential for the pointer to be NULL. However, later in the function we have:

case VBOXGUEST_IOCTL_GUEST_CAPS_ACQUIRE:

CHECKRET_SIZE("GUEST_CAPS_ACQUIRE", sizeof(VBoxGuestCapsAquire)); rc = vgdrvIoCtl_GuestCapsAcquire(pDevExt, pSession, (VBoxGuestCapsAquire *)pvData); *pcbDataReturned = sizeof(VBoxGuestCapsAquire); break;

and this dereferencing the pointer that could potentially be zero.