do not override nGlobalError with error from ConvertStringToValue()

... so an already existing previous error is kept.

Change-Id: Ie731f17e93afa512542cc3ba2378031e978f9462
(cherry picked from commit df149997849c1e07d735fdeefccf875e7361aa4c)
Reviewed-on: https://gerrit.libreoffice.org/26338
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>
diff --git a/sc/source/core/tool/interpr4.cxx b/sc/source/core/tool/interpr4.cxx
index 6324103..812409e 100644
--- a/sc/source/core/tool/interpr4.cxx
+++ b/sc/source/core/tool/interpr4.cxx
@@ -187,10 +187,11 @@ sal_uInt16 ScInterpreter::GetCellErrCode( const ScRefCellValue& rCell )

double ScInterpreter::ConvertStringToValue( const OUString& rStr )
{
    double fValue = ScGlobal::ConvertStringToValue( rStr, maCalcConfig, nGlobalError, mnStringNoValueError,
    sal_uInt16 nError = 0;
    double fValue = ScGlobal::ConvertStringToValue( rStr, maCalcConfig, nError, mnStringNoValueError,
            pFormatter, nCurFmtType);
    if (nGlobalError)
        SetError(nGlobalError);
    if (nError)
        SetError(nError);
    return fValue;
}