INT 21 u - LAN Manager Enhanced DOS - DosReadMailslot                           
	AX = 5F50h
	BX = handle
	DX:CX = timeout
	ES:DI -> buffer
Return: CF clear if successful
	    AX = bytes read
	    CX = next item's size
	    DX = next item's priority
	CF set on error
	    AX = error code
SeeAlso: AX=5F4Dh,AX=5F4Fh,AX=5F51h,AX=5F52h