Bug 1058399 - Fix VideoData leak on osx fmp4 seek. r=cpearce

Calling Clear() on the reorder queue doesn't call delete on
the stored pointer elements. Do this explicitly to avoid leaking
decoded frames when ::Flush() is called.
Bug 1058400 - Fix AppleCMLinker assertion. r=cpearce

We call Unlink() from the failure cleanup code in Link() when
the dlopen call fails, so it's incorrect to assert that sLink
is non-null. We've already incremented the refcount, so that
check is fine.