Zero end of embedded block buffer in dump_write_embedded()
This fixes a kernel stack leak.
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Tested-by: Nicholas Sherlock <n.sherlock@gmail.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13778
Closes #14255