Get the address of a previously-allocated general scratchpad to retain data between iterations of a local table function copy.
FNC_TblGetCtx returns the address of the general scratchpad that a local table function copy can use to retain data between iterations.
The return value is a NULL pointer if the general scratchpad has not been previously allocated with a call to FNC_TblAllocCtx.
This library function is valid during any mode or processing phase in which the table function is invoked.