INT 21 - DOS 1+ - FIND FIRST MATCHING FILE USING FCB
        AH = 11h
        DS:DX -> unopened FCB (see AH=0Fh), may contain '?' wildcards
Return: AL = status
            00h successful
                [DTA] unopened FCB for first matching file
            FFh no matching filename, or bad FCB
Notes:  the type of the returned FCB depends on whether the input FCB was a
          normal or an extended FCB
        the data returned in the DTA is actually the drive number (or extended
          FCB header and drive number) followed by the file's directory entry
          (see below); this format happens to be compatible with an unopened
          FCB
        for extended FCBs with search attribute 08h, the volume label (if any)
          will be returned even if the current directory is not the root dir.
        DOS 3+ also allows the '*' wildcard
        the search FCB must not be modified if AH=12h will be used to continue
          searching; DOS 3.3 has set the following parts of the FCB:
                 0Ch    BYTE    ???
                 0Dh    WORD    directory entry number of matching file
                 0Fh    WORD    cluster number of current directory
                 11h  4 BYTEs   ???
                 15h    BYTE    drive number (1=A:)
        this function is used by many copy protection schemes to obtain the
          starting cluster of a file
SeeAlso: AH=12h,AH=1Ah,AH=4Eh,INT 2F/AX=111Bh

Format of directory entry:
Offset  Size    Description
 00h  8 BYTEs   blank-padded filename
 08h  3 BYTEs   blank-padded file extension
 0Bh    BYTE    attributes
 0Ch 10 BYTEs   reserved
                used by DR-DOS to store file password
 16h    WORD    time of creation or last update (see AX=5700h)
 18h    WORD    date of creation or last update (see AX=5700h)
 1Ah    WORD    starting cluster number
 1Ch    DWORD   file size

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