ZILBTC SPOT aggtrades Duplicated aggtradeid

There's a duplicated aggtradeid (12027555) for ZILBTC although they refer to different tradeids (20090669 and 20090670)

```
tail ZILBTC-aggTrades-2021-02-28.csv
_12027546,0.00000238,2082.00000000,20090650,20090657,1614556630707,True,True
12027547,0.00000238,418.00000000,20090658,20090658,1614556665519,False,True
12027548,0.00000238,1164.00000000,20090659,20090660,1614556667888,False,True
12027549,0.00000239,2749.00000000,20090661,20090661,1614556667888,False,True
12027550,0.00000238,2810.00000000,20090662,20090662,1614556726384,False,True
12027551,0.00000238,747.00000000,20090663,20090663,1614556738998,True,True
12027552,0.00000238,3233.00000000,20090664,20090666,1614556749346,True,True
12027553,0.00000238,81.00000000,20090667,20090667,1614556770832,False,True
12027554,0.00000238,296.00000000,20090668,20090668,1614556777314,False,True
12027555,0.00000238,824.00000000,**20090669,20090669**,1614556777324,False,True
```

```
head ZILBTC-aggTrades-2021-03-01.csv
12027555,0.00000239,19332.00000000,**20090670,20090670**,1614556823276,False,True
12027556,0.00000239,6277.00000000,20090671,20090681,1614556860776,False,True
12027557,0.00000239,4405.00000000,20090682,20090686,1614556916896,False,True
12027558,0.00000239,103.00000000,20090687,20090687,1614556924758,False,True
12027559,0.00000238,268.00000000,20090688,20090688,1614556930592,True,True
12027560,0.00000238,401.00000000,20090689,20090689,1614556953506,True,True
12027561,0.00000239,334.00000000,20090690,20090691,1614557045617,False,True
12027562,0.00000239,1691.00000000,20090692,20090692,1614557053189,False,True
12027563,0.00000239,3349.00000000,20090693,20090695,1614557067793,False,True
12027564,0.00000238,50048.00000000,20090696,20090704,1614557105252,True,True
```

I would expect aggtradeid per symbol to be unique. Perhaps this one should be aggregated in one including 20090669 and 20090670?

Start by comparing the adjacent records in ZILBTC-aggTrades-2021-02-28.csv and ZILBTC-aggTrades-2021-03-01.csv, focusing on aggtradeid 12027555 and tradeids 20090669-20090670. Check whether the duplicate reflects an error in the published historical data or an expected aggregation rule; done means documenting the determination and correcting or clarifying the affected records.

Written by the indexing model from the issue text.