Fix crash from FillRateLogging

Reviewed By: thechefchen

Differential Revision: D4853991

fbshipit-source-id: b024d4052edb04e9f9da2e2504c56f8b7840cded

Libraries/Lists/FillRateHelper.js

@@ -108,6 +108,9 @@ class FillRateHelper {
       return null;
     }
     const start = performanceNow();
+    if (props.getItemCount(props.data) === 0) {
+      return null;
+    }
     if (!this._samplesStartTime) {
       this._samplesStartTime = start;
     }