need fix small error

[quanpm4900]

in below function add m_pFmDemod = NULL;
(file dsp/demodulation.cpp)
CDemodulator::CDemodulator()
{
m_DesiredMaxOutputBandwidth = 48000.0;
m_OutputRate = 48000.0;
m_pDemodInBuf = new TYPECPX[MAX_INBUFSIZE];
m_pDemodTmpBuf = new TYPECPX[MAX_INBUFSIZE];
m_InBufPos = 0;
m_InBufLimit = 1000;
m_DemodMode = -1;
m_pAmDemod = NULL;
m_pSamDemod = NULL;
m_pSsbDemod = NULL;
SetDemodFreq(0.0);
}