Fixes functions for checking and parsing of texture attribute files

- The checking texture attribute file functions has been fixed to
return the name of the attribute file rather than the graphic file.
- The texture attribute file parser now uses the layout defined prior
to OpenFlight v16.1 and above. From v16.1, an additional 8 bytes of
reserved space exists causing a possible offset when reading data.
- Texture attribute file parser function now handles file parsing error
better. Such errors are likely going to occur when an attribute file
terminates earlier than expected. The function will now display a
warning and allow the parent function to continue parsing further
opcodes.
- Fixed ReadFile function which was still passing a filename to opcode
functions despite having removed input arguments for opcode functions.
- Numerous syntax errors and small bugs have been fixed.