Fix array splice in task intercepting for-of loop
Fix array splice in task intercepting for-of loop

Two issues exist in old code:
1. It is unsafe to do array splice in for-of loop
2. Array splicing for one task may be triggered by multiple interceptors
without checking task existence in array

lsxiao/qiniu4js,lsxiao/qiniu4js,lsxiao/qiniu4js