[ft] Question about FT_Get_Sfnt_Name

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Hello.

I
 have a question about FT_Get_Sfnt_Name. The official documentation 
about this 
function(https://www.freetype.org/freetype2/docs/reference/ft2-sfnt_names.html#FT_Get_Sfnt_Name)
 gives the following information:

The ??string?? array returned in the ??aname?? structure is not 
null-terminated. The application should deallocate it if it is no longer
 in use.

However, every time I try to free the string, it always causes a double-free error. The error prompts say something like this:
Error in `./testsample': double free or corruption (fasttop): 0x00000000023ff9e0

My code is as simple as the following:
FT_SfntName  name;
FT_Get_Sfnt_Name(face, i, &name);
free(name.string); //This line causes a double-free error.

I think the documentation is clear enough about who is responsible for 
deallocating the 'string' array, or do I misunderstand something in the 
documentation?

Thank you in advance.