textproc/aspell: fix build with clang 19

With clang 19 and gcc 15, textproc/aspell fails to compile, with errors
similar to:

    In file included from modules/speller/default/readonly_ws.cpp:51:
    modules/speller/default/vector_hash-t.hpp:186:43: error: no member named 'e'
in 'VectorHashTable<Parms>'
      186 |     for (iterator i = begin(); i != this->e; ++i, ++this->_size);
          |                                     ~~~~  ^
    modules/speller/default/vector_hash-t.hpp:186:59: error: no member named
'_size' in 'VectorHashTable<Parms>'; did you mean 'size_'?
      186 |     for (iterator i = begin(); i != this->e; ++i, ++this->_size);
          |                                                           ^~~~~
          |                                                           size_
    modules/speller/default/vector_hash.hpp:182:17: note: 'size_' declared here
      182 |     size_type   size_;