Fix a out of bound buffer access in ParsingUtils GetNextLine (#6134)

include/assimp/ParsingUtils.h

@@ -161,7 +161,7 @@ AI_FORCE_INLINE bool GetNextLine(const char_t *&buffer, char_t out[BufferSize])
     }
 
     char *_out = out;
-    char *const end = _out + BufferSize;
+    char *const end = _out + BufferSize - 1;
     while (!IsLineEnd(*buffer) && _out < end) {
         *_out++ = *buffer++;
     }