builtin/merge.c - cleanup of code in for-cycle that tests strategies

builtin/merge.c - cleanup of code in for-cycle that tests strategies

The cmd_merge() function has a loop that tries different
merge strategies in turn, and stops when a strategy gets a
clean merge, while keeping the "best" conflicted merge so
far.

Make the loop easier to follow by moving the code around,
ensuring that there is only one "break" in the loop where
an automerge succeeds.  Also group the actions that are
performed after an automerge succeeds together to a single
location, outside and after the loop.

Signed-off-by: Edmundo Carmona Antoranz <eantoranz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>