Fix #190: clear entire quantized coefficient buffer

Clear entire buffer to ensure all values in the buffer are valid
even though some values may lie outside the subset of coefficients
that is effectively coded

source/Lib/CommonLib/QuantRDOQ.cpp

@@ -676,6 +676,7 @@ void QuantRDOQ::xRateDistOptQuant(TransformUnit &tu, const ComponentID &compID,
   TCoeff *deltaU       = m_deltaU;
 #endif
 
+  memset(piDstCoeff, 0, sizeof(*piDstCoeff) * uiMaxNumCoeff);
   memset( m_pdCostCoeff,  0, sizeof( double ) *  uiMaxNumCoeff );
   memset( m_pdCostSig,    0, sizeof( double ) *  uiMaxNumCoeff );
 #if HEVC_USE_SIGN_HIDING