fdo#72521 fdo#73103 Fix editable combo-boxes behavior under KDE4

Change-Id: I92a781a1e0f0adcb779155f8c477595e0dd762b1
Reviewed-on: https://gerrit.libreoffice.org/7287Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Tested-by: Jan-Marek Glogowski <glogow@fbihome.de>

vcl/unx/kde4/KDESalGraphics.cxx

@@ -779,7 +779,11 @@ sal_Bool KDESalGraphics::getNativeControlRegion( ControlType type, ControlPart p
                     break;
                 }
                 case PART_BUTTON_DOWN:
-                    //the entire control can be used as the "down" button
+                    contentRect = kapp->style()->subControlRect(
+                        QStyle::CC_ComboBox, &cbo, QStyle::SC_ComboBoxArrow );
+
+                    contentRect.translate( boundingRect.left(), boundingRect.top() );
+
                     retVal = true;
                     break;
                 case PART_SUB_EDIT: