Compatibility: XMS 2.0+
Expects: AH    0cH
DX    XMS handle (as obtained via XMS 09H)
Returns: AX    status: 0000H = successful
0001H = error and BL=XMS error code (if BL >= 80H)
DX:BX 32-bit linear address of base of block
Info: This locks an extended memory block into place (XMM will not move
its data around while locked) and returns a 32-bit linear address
of the start of the block.

The block should be unlocked as soon as possible (see XMS 0dH).

The XMM maintains a "lock-count" and only allows the block to
move when the lock count is decremented to 0.  XMS 0eH obtains
the current lock count.

See Also: XMS Functions
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XMS 0cH: Lock Extended Memory Block