Fix the bug because of enqueueing an unchecked commit task

[TheR1sing3un]

case:

n1(leader) : | 0| 1| 2| 3| 4|
n2(follower): | 0| 1| 2| 3| 4|
n3(follower): | 0|

n1 will append log[1] and commitIndex[4] to n3.

n3 will append log[1], and directly enqueue a commit task with commitIndex[4] to stm caller.

now logs in n3 like that:
n3(follower): | 0| 1|

stm will apply task iterator from lastAppliedIndex[0] to commitIndex[4]

but n3 only has logs up to index[1], so it will failed because of visit log which is out of range