fix stats task_index after negative-index repair

meta/stats.json

@@ -1068,25 +1068,25 @@
       0.0
     ],
     "std": [
-      -1.0
+      0.0
     ],
     "count": [
-      34999.0
+      34999
     ],
     "q01": [
-      2.220446049250313e-16
+      0.0
     ],
     "q10": [
-      4.440892098500626e-15
+      0.0
     ],
     "q50": [
-      1.9761969838327786e-14
+      0.0
     ],
     "q90": [
-      3.530509218307998e-14
+      0.0
     ],
     "q99": [
-      3.9968028886505635e-14
+      0.0
     ]
   }
 }