l path file name from a given buffer ID.
<p>Return -1 if the bufferID non existing, otherwise the number of TCHAR copied/to copy.
User should call it with fullFilePath be NULL to get the number of TCHAR (not including the nul character), allocate fullFilePath with the return values + 1, then call it again to get full path file name 
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<td width="50%" rowspan="2" style="background:LightYellow;">  NPPM_GETBUFFERIDFROMPOS
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<td widt