MFV r344878:

4.2.8p12 --> 4.2.8p13

MFC after: immediately
Security: CVE-2019-8936
VuXML: c2576e14-36e2-11e9-9eda-206a8a720317
Obtained from: nwtime.org

MFV ntp 4.2.8p1 (r258945, r275970, r276091, r276092, r276093, r278284)

Thanks to roberto for providing pointers to wedge this into HEAD.

Approved by: roberto