demodatv: initialize uninitialized sync detection members

Initialize the field and vertical sync detection sample counters and
the previous sample value in ATVDemodSink.

This gives the video synchronization state defined initial values when
the sink is constructed and removes the uninitialized member warnings
reported by cppcheck.

Signed-off-by: Robin Getz <rgetz503@gmail.com>

plugins/channelrx/demodatv/atvdemodsink.cpp

@@ -38,6 +38,8 @@ ATVDemodSink::ATVDemodSink() :
     m_numberSamplesPerHTop(0),
     m_fieldIndex(0),
     m_synchroSamples(0),
+    m_fieldDetectSampleCount(0),
+    m_vSyncDetectSampleCount(0),
     m_effMin(20.0f),
     m_effMax(-20.0f),
     m_ampMin(-1.0f),
@@ -50,6 +52,7 @@ ATVDemodSink::ATVDemodSink() :
     m_lineIndex(0),
 	m_hSyncShift(0.0f),
     m_hSyncErrorCount(0),
+    prevSample(0.0f),
     m_ampAverage(4800),
     m_bfoPLL(200/1000000, 100/1000000, 0.01),
     m_bfoFilter(200.0, 1000000.0, 0.9),