Resolve some TODO comments

- `out_PushSection` should not set `currentSection` to NULL because
  PUSHS, PUSHC, and PUSHO consistently keep the current section,
  charmap, and options, even though the stack has been pushed.

- `Callback__FILE__` does not need to assert that `fileName` is not
  empty because `__FILE__`'s value is quoted, and can safely be empty.

- `YY_FATAL_ERROR` and `YYLMAX` are not needed since the lexer is
  not generated with flex.

include/asm/lexer.h

@@ -53,7 +53,7 @@ static inline void lexer_SetGfxDigits(char const digits[4])
  * `path` is referenced, but not held onto..!
  */
 struct LexerState *lexer_OpenFile(char const *path);
-struct LexerState *lexer_OpenFileView(char *buf, size_t size, uint32_t lineNo);
+struct LexerState *lexer_OpenFileView(char const *path, char *buf, size_t size, uint32_t lineNo);
 void lexer_RestartRept(uint32_t lineNo);
 void lexer_DeleteState(struct LexerState *state);
 void lexer_Init(void);