debugger: fix QHashNode dumper and QHashNode type check for Qt4

The previous workaround for the Qt 4 optimized int,uint,short,ushort
QHashNode wasn't working for the QHashNode dumper itself because of
unknown key type. Instead we first try to find the 'key' child directly,
if that fails we look for it in the second child (which would be the
anonymous union from the optimized hash node, which contains the key).

Also fix the expected type for QHashNode in the optimized case for Qt4

Change-Id: Ib48c2c0afec081ff38cd750c3d515a5e678e9661
Reviewed-by: hjk <hjk121@nokiamail.com>