99h FL$VALX get file type from extension
Input X register - points to ".ext".
B register - length of extension.
Output A register - file type for extension at x.
UTW_S0+1 - 1 if OPO, 2 if OPT, 0 otherwise.

Returns A as file type for extension at X (points to ".") length B.

If X points to ".*", returns A=0. If B is passed as 0, returns A=$FF.

This call is not available on CM/XP machines.

Errors 236 - bad file name