Description: fix a fencepost error in pipe_advance()
References:
Notes:
 jmm> According to commit message only affecting 4.9
Bugs:
upstream: released (4.10-rc4) [b9dc6f65bc5e232d1c05fe34b5daadc7e8bbf1fb]
3.16-upstream-stable: N/A "Vulnerability introduced in 4.9 with 241699cd72a8489c9446ae3910ddd243e9b9061b"
3.2-upstream-stable: N/A "Vulnerability introduced in 4.9 with 241699cd72a8489c9446ae3910ddd243e9b9061b"
sid: released (4.9.6-1)
3.16-jessie-security: N/A "Vulnerability introduced in 4.9 with 241699cd72a8489c9446ae3910ddd243e9b9061b"
3.2-wheezy-security: N/A "Vulnerability introduced in 4.9 with 241699cd72a8489c9446ae3910ddd243e9b9061b"