fix ilistbox dispose.

Change-Id: Icc5b6e924dfeec7a7da4f654d79b17fe91ce1418

vcl/source/control/combobox.cxx

@@ -74,7 +74,11 @@ ComboBox::~ComboBox()
 void ComboBox::dispose()
 {
     mpSubEdit.disposeAndClear();
-    mpImplLB.disposeAndClear();
+
+    VclPtr< ImplListBox > pImplLB = mpImplLB;
+    mpImplLB.clear();
+    pImplLB.disposeAndClear();
+
     mpFloatWin.disposeAndClear();
     mpBtn.disposeAndClear();
     Edit::dispose();

vcl/source/control/ilstbox.cxx

@@ -2174,10 +2174,9 @@ ImplListBox::~ImplListBox()
 
 void ImplListBox::dispose()
 {
-    mpHScrollBar.clear();
-    mpVScrollBar.clear();
-    mpScrollBarBox.clear();
-    maLBWindow.clear();
+    mpHScrollBar.disposeAndClear();
+    mpVScrollBar.disposeAndClear();
+    mpScrollBarBox.disposeAndClear();
     maLBWindow.disposeAndClear();
     Control::dispose();
 }