readPointer == writePointer when samples are lost

[solarjoe]

This line

int8_t numberOfSamples = sense.head - sense.tail;

or this one

numberOfSamples = writePointer - readPointer;

do not seem to work if samples are lost. In this case both pointers seem so point to the same location and the number of samples results to 0. But the FIFO is full.