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INT 21h/4401h should report invalid function for nonzero DH #266

Description

@nakatamaho

Expected behavior

The MS-DOS 4.0 Programmer's Reference, INT 21h Function 44h, codes 00h/01h requires DH=0 for AL=01h and lists AX=1 when AL=01h is called with DH nonzero.

Current source behavior

At lpproj/fdkernel commit ac16c8a7401526f99787e03babdb2f4223d48fc4, DosDevIOctl() returns DE_INVLDDATA for a nonzero DH in the AL=01h path. This exposes error 13 instead of the documented error 1.

Please confirm whether FreeDOS intentionally differs from the documented DOS contract here. If not, consider returning invalid function for this invalid AL/DH combination. The conformance fixture keeps the reference-based AX=1 expectation.

The comparison uses only the public source revision and public reference; it contains no private media or trace data.

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