libpurpleAdapter: fix build on qemux86-64

* otherwise it fails with:
  imlibpurpleservice/3.0.5+gitrAUTOINC+8a6684e396-r0/git/src/LibpurpleAdapter.cpp:970:81:
  error: cast from 'gpointer {aka void*}' to 'guint {aka unsigned int}' loses precision [-fpermissive]
  |   guint timerHandle = (guint)g_hash_table_lookup(s_accountLoginTimers, accountKey);

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>