Set the messages to accurately reflect what is being tested, make them
unique and trace bad values.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=55354

When the sample size is too small, we were releasing it from the memory,
but kept the next_sample pointer set. Later, when the transform removes
the sample from the allocator, its refcount was decremented one more
time, effectively leaking the sample.