stringToDouble() do not parse separator without digit as 0.0

Occurred in CSV import without "detect special numbers" activated for data like
,.,
where the . dot resulted in a numeric cell value 0

Change-Id: Ie715d7a8ed02196b59968a92919ad286b3bedf64
diff --git a/sal/rtl/math.cxx b/sal/rtl/math.cxx
index 92de8b6..c694e58 100644
--- a/sal/rtl/math.cxx
+++ b/sal/rtl/math.cxx
@@ -694,6 +694,7 @@ inline double stringToDouble(CharT const * pBegin, CharT const * pEnd,
        while (p != pEnd && (*p == CharT('0') || *p == cGroupSeparator))
            ++p;

        CharT const * pFirstSignificant = p;
        long nValExp = 0;       // carry along exponent of mantissa

        // integer part of mantissa
@@ -741,7 +742,19 @@ inline double stringToDouble(CharT const * pBegin, CharT const * pEnd,
            if ( fFrac != 0.0 )
                fVal += rtl::math::pow10Exp( fFrac, nFracExp );
            else if ( nValExp < 0 )
            {
                if (pFirstSignificant + 1 == p)
                {
                    // No digit at all, only separator(s) without integer or
                    // fraction part. Bail out. No number. No error.
                    if (pStatus != nullptr)
                        *pStatus = eStatus;
                    if (pParsedEnd != nullptr)
                        *pParsedEnd = pBegin;
                    return fVal;
                }
                nValExp = 0;    // no digit other than 0 after decimal point
            }
        }

        if ( nValExp > 0 )