Found by Volker, patch to follow.
Created attachment 14443 [details] git-am fix for 4.9.next, 4.8.next, 4.7.next.
Comment on attachment 14443 [details] git-am fix for 4.9.next, 4.8.next, 4.7.next. Cherry-picked from master.
Pushed to autobuild-v4-{9,8,7}-test.
Pushed to all branches. Closing out bug report. Thanks!