Cdbext: Fix QMap dumper for Qt5...

... when the symbol was added as an expression.

It seems that calling GetSymbolTypeName somehow destroys the red-black tree,
so moved the call before creating the tree.

Change-Id: Iefb187df4e7f99cfd95195a6ac9a4d8c64fa2365
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>