INT 21 - DOS 1+ - GET FILE SIZE FOR FCBsee File Control Block
	AH = 23h
	DS:DX -> unopened FCBsee File Control Block (see #01345), wildcards not allowed
Return: AL = status
	    00h successful (matching file found)
		FCBsee File Control Block random record field filled with size in records, rounded up
		to next full record
	    FFh failed (no matching file found)
Notes:	not supported by MS Windows 3.0 DOSX.EXE DOS extender
	MS-DOS returns nonsense if the FCBsee File Control Block record number field is set to a very
	  large positive number, and status FFh if negative; DR DOS returns the
	  correct file size in both cases
BUG:	APPEND for DOS 3.3+ corrupts DX if the file is not found
SeeAlso: AH=42h