Fix playback within Sample (#7100)

This revisits two main aspects of playback from `Sample`: copying frames into a temporary playback buffer before resampling, and advancing the state's frame index.  Both operations were improperly done, causing distorted audio to be heard when resampling from within the `Sample::play` function.

To fix this, playback into the temporary playback buffer is now done using the `playRaw` function, which copies the frame one by one in a loop, moving through the buffer correctly as determined by the loop mode. In addition, advancement of the playback index is done using the `advance` function, which advances the index by the given amount and handles an out of bounds index for the loop modes as necessary using the modulo operator.

src/core/SampleBuffer.cpp

@@ -31,7 +31,7 @@
 
 namespace lmms {
 
-SampleBuffer::SampleBuffer(const sampleFrame* data, int numFrames, int sampleRate)
+SampleBuffer::SampleBuffer(const sampleFrame* data, size_t numFrames, int sampleRate)
 	: m_data(data, data + numFrames)
 	, m_sampleRate(sampleRate)
 {