Function  23h  Get File Size						 (FCB)
 Searches current subdirectory for matching file, returns size in Struct -FCB
entry	AH	23h
	DS:DX	address of an unopened Struct -FCB
return  AL      00h file found 
		0FFh file not found 
note 1) Record size field (offset 0Eh) must be set before invoking this function 
     2) The disk directory is searched for the matching entry. If a matching 
	entry is found, the random record field is set to the number of records 
	in the file. If the value of the Record Size field is not an even 
	divisor of the file size, the value set in the relative record field is  
	rounded up. This gives a returned value larger than the actual file size 
     3) This call is used by the APPEND command in DOS 3.2+