rerere: fix an off-by-one non-bug

rerere: fix an off-by-one non-bug

When ac49f5ca (rerere "remaining", 2011-02-16) split out a new
helper function check_one_conflict() out of find_conflict()
function, so that the latter will use the returned value from the
new helper to update the loop control variable that is an index into
active_cache[], the new variable incremented the index by one too
many when it found a path with only stage #1 entry at the very end
of active_cache[].

This "strange" return value does not have any effect on the loop
control of two callers of this function, as they all notice that
active_nr+2 is larger than active_nr just like active_nr+1 is, but
nevertheless it puzzles the readers when they are trying to figure
out what the function is trying to do.

In fact, there is no need to do an early return.  The code that
follows after skipping the stage #1 entry is fully prepared to
handle a case where the entry is at the very end of active_cache[].

Help future readers from unnecessary confusion by dropping an early
return.  We skip the stage #1 entry, and if there are stage #2 and
stage #3 entries for the same path, we diagnose the path as
THREE_STAGED (otherwise we say PUNTED), and then we skip all entries
for the same path.

Signed-off-by: Junio C Hamano <gitster@pobox.com>