C++: Fix duplicate items in C++ completion for Qt methods

C++: Fix duplicate items in C++ completion for Qt methods

In the old code completion engine items were created on the stack
and passed around by value. With the refactoring of the code assist
API they became heap objects manipulated through pointers. This
patch fixes one reminiscence not caught during the refactoring
in which the same actual pointer was being used more than once to
be appended on the list.

Change-Id: I2009fb0b6aa18df57aa5ca9bde0591536ca2cd74
Reviewed-on: http://codereview.qt-project.org/4444
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>