community/ftgl: fix build with gcc 14

Fix type conversion error with gcc 14 and freetype.

```
FTVectoriser.cpp: In member function 'void FTVectoriser::ProcessContours()':
FTVectoriser.cpp:171:25: error: invalid conversion from 'unsigned char*'
to 'char*' [-fpermissive]
  171 |         char* tagList = &outline.tags[startIndex];
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
      |                         |
      |                         unsigned char*
```