Fix unit test failure

The recent commit 022b564831, which added
a few source files to kitemlistcontrollertest, caused a crash in that
test - an assert was hit because now a different virtual method was
called in one place (KStandardItemListView::initializeItemListWidget()),
and qobject_cast could not cast the 'item', which is of type
KFileItemListWidget, to its base class KStandardItemListWidget. Adding
the source file kfileitemlistwidget.cpp fixes this.

CCMAIL: ps_ml@gmx.de

src/tests/CMakeLists.txt

@@ -18,6 +18,7 @@ set(kitemlistcontrollertest_SRCS
     testdir.cpp
     ../kitemviews/kfileitemmodel.cpp
     ../kitemviews/kfileitemlistview.cpp
+    ../kitemviews/kfileitemlistwidget.cpp
     ../kitemviews/kitemmodelbase.cpp
     ../kitemviews/kitemlistview.cpp
     ../kitemviews/kitemlistcontainer.cpp