Return the ascii value of a specified character in a string
──────────────────────────────────────────────────────────────────────────────

 Syntax

        GT_Ascpos(<cStr>, <nPos>) --> nAscVal

 Arguments:

      <cStr>  - The string
      <nPos>  - The position in <cStr>

 Returns:

      nAscVal - The ascii value of substr(<cStr>, <nPos>, 1)

 Description:

      Return the ascii value of a specified character in a string
      Equivalent (but much faster) to
          asc(substr(cStr, nPos, 1)

      NOTE:
         invalid parameters will return -1
         nPos > len(cStr)   will return -2

      This last behaviour is different to the Funcky function of the
      same name.  I changed the behaviour because some of the strings
      I process contain embedded NULs.

 Examples:

       ? gt_ascpos("the cat sat on the mat", 3)
                                   // prints e

 Source: ASCPOS.C

 Author:  Andy M Leighton