log: consolidate the commited entry rewrite check

The append function call right after this does the same check, we don't
need to do this in two places. TestLogMaybeAppend exercises these
panics, and confirms the behaviour is the same after the first panic is
removed.

Signed-off-by: Pavel Kalinnikov <[email protected]>

log.go

@@ -109,9 +109,6 @@ func (l *raftLog) maybeAppend(a logSlice, committed uint64) (lastnewi uint64, ok
 	if !ok {
 		return 0, false
 	}
-	if match.index < a.lastIndex() && match.index < l.committed {
-		l.logger.Panicf("entry %d is already committed [committed(%d)]", match.index+1, l.committed)
-	}
 
 	// Fast-forward to the first mismatching or missing entry.
 	// NB: prev.index <= match.index <= a.lastIndex(), so the sub-slicing is safe.
@@ -129,8 +126,8 @@ func (l *raftLog) append(ents ...pb.Entry) uint64 {
 	if len(ents) == 0 {
 		return l.lastIndex()
 	}
-	if after := ents[0].Index - 1; after < l.committed {
-		l.logger.Panicf("after(%d) is out of range [committed(%d)]", after, l.committed)
+	if mismatch := ents[0].Index; mismatch <= l.committed {
+		l.logger.Panicf("entry %d is already committed [committed(%d)]", mismatch, l.committed)
 	}
 	l.unstable.truncateAndAppend(ents)
 	return l.lastIndex()