Always use split button for .uno:CharBackColor

Change-Id: I4dd01ec8692fff77a94d6fa698e438581f6dbf37
diff --git a/svx/source/tbxctrls/tbcontrl.cxx b/svx/source/tbxctrls/tbcontrl.cxx
index efedc30..7854060 100644
--- a/svx/source/tbxctrls/tbcontrl.cxx
+++ b/svx/source/tbxctrls/tbcontrl.cxx
@@ -2778,6 +2778,7 @@ SvxColorToolBoxControl::SvxColorToolBoxControl(
            SAL_FALLTHROUGH;

        case SID_ATTR_CHAR_COLOR:
        case SID_ATTR_CHAR_BACK_COLOR:
            m_bSplitButton = true;
            break;