Merge branch 'jc/am-3-fallback-regression-fix' into maint

"git am -3" had a small regression where it is aborted in its error handling codepath when underlying merge-recursive failed in certain ways, as it assumed that the internal call to merge-recursive will never die, which is not the case (yet). * jc/am-3-fallback-regression-fix: am -3: do not let failed merge from completing the error codepath