debugger: fix display of QStringList after a takeFirst();

(cherry picked from commit f9e6a963)

share/qtcreator/gdbmacros/gdbmacros.py

@@ -1421,6 +1421,7 @@ def qdump__QStringList(d, item):
     if d.isExpanded(item):
         innerType = gdb.lookup_type(d.ns + "QString")
         ptr = gdb.Value(d_ptr["array"]).cast(innerType.pointer())
+        ptr += d_ptr["begin"]
         with Children(d, [size, 1000], innerType):
             for i in d.childRange():
                 d.putItem(Item(ptr.dereference(), item.iname, i))

tests/manual/gdbdebugger/simple/app.cpp

@@ -1200,6 +1200,7 @@ void testQStringList()
     l << "Hello ";
     l << " big, ";
     l << " fat ";
+    l.takeFirst();
     l << " World ";
 }