SampleRecordHandle: Obtain the offset to the record with a parameter

instead of hacking sampleBuffer ()->startFrame ().

That solves a bug with `startFrame ()` being negetive in recording some
cases.

include/SampleRecordHandle.h

@@ -41,7 +41,7 @@ class Track;
 class SampleRecordHandle : public PlayHandle
 {
 public:
-	SampleRecordHandle( SampleTCO* tco );
+	explicit SampleRecordHandle(SampleTCO* tco, TimePos startRecordTimeOffset);
 	virtual ~SampleRecordHandle();
 
 	void play( sampleFrame * _working_buffer ) override;
@@ -65,7 +65,10 @@ private:
 	Track * m_track;
 	BBTrack * m_bbTrack;
 	SampleTCO * m_tco;
-
+	
+	// The offset from the start of m_track that the record has
+	// started from.
+	TimePos m_startRecordTimeOffset;
 } ;
 
 

src/core/SampleRecordHandle.cpp

@@ -33,13 +33,14 @@
 #include "debug.h"
 
 
-SampleRecordHandle::SampleRecordHandle( SampleTCO* tco ) :
+SampleRecordHandle::SampleRecordHandle(SampleTCO* tco , TimePos startRecordTimeOffset) :
 	PlayHandle( TypeSamplePlayHandle ),
 	m_framesRecorded( 0 ),
 	m_minLength( tco->length() ),
 	m_track( tco->getTrack() ),
 	m_bbTrack( nullptr ),
-	m_tco( tco )
+	m_tco(tco),
+	m_startRecordTimeOffset{startRecordTimeOffset}
 {
 }
 
@@ -53,6 +54,8 @@ SampleRecordHandle::~SampleRecordHandle()
 		SampleBuffer* sb;
 		createSampleBuffer( &sb );
 		m_tco->setSampleBuffer( sb );
+
+		m_tco->setStartTimeOffset(m_startRecordTimeOffset);
 	}
 	
 	while( !m_buffers.empty() )

src/tracks/SampleTrack.cpp

@@ -144,7 +144,7 @@ bool SampleTrack::play( const TimePos & _start, const fpp_t _frames,
 				{
 					return played_a_note;
 				}
-				SampleRecordHandle* smpHandle = new SampleRecordHandle( st );
+				SampleRecordHandle* smpHandle = new SampleRecordHandle( st , _start - st->startPosition ());
 				handle = smpHandle;
 			}
 			else