do not ignore return value of a (confusing) function (tdf#126248)

The two ScCellFormat::GetString() overloads are lame API, one returns
the value normally and the other one returns void and uses a reference
parameter. I got confused by this in 6f810e3d7dafcd7d0101173a501
and didn't use the return value in one case.

Change-Id: I0b6c839f9d0299e14ea022813481802275df5ea6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/86750
Tested-by: Jenkins
Reviewed-by: 锁琨珑 <suokunlong@126.com>
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
diff --git a/sc/source/core/data/documen6.cxx b/sc/source/core/data/documen6.cxx
index 789f26c..e6d7a31 100644
--- a/sc/source/core/data/documen6.cxx
+++ b/sc/source/core/data/documen6.cxx
@@ -120,7 +120,7 @@ SvtScriptType ScDocument::GetCellScriptType( const ScAddress& rPos, sal_uInt32 n
    if( pCell )
        ScCellFormat::GetString(*pCell, nNumberFormat, aStr, &pColor, *mxPoolHelper->GetFormTable(), this);
    else
        ScCellFormat::GetString(*this, rPos, nNumberFormat, &pColor, *mxPoolHelper->GetFormTable());
        aStr = ScCellFormat::GetString(*this, rPos, nNumberFormat, &pColor, *mxPoolHelper->GetFormTable());

    SvtScriptType nRet = GetStringScriptType( aStr );