fix for missing rows in ManagedTable

Summary:
When starting with an empty table and adding rows, the scrollOffset of the table might end up with a negative value, which causes rows not to be rendered.

See https://github.com/bvaughn/react-window/issues/49 for more details.

This only calls `scrollToItem` when the table is actually scrollable to prevent a negative scrollOffset.

Reviewed By: passy

Differential Revision: D9570518

fbshipit-source-id: 5b08990a353a6d41d0f1bc5c1481d5a5e471bd94

src/ui/components/table/ManagedTable.js

@@ -272,9 +272,19 @@ class ManagedTable extends React.Component<
   };
 
   scrollToBottom() {
-    const {current} = this.tableRef;
+    const {current: tableRef} = this.tableRef;
-    if (current && this.props.rows.length > 1) {
+    const {current: scrollRef} = this.scrollRef;
-      current.scrollToItem(this.props.rows.length - 1);
+    if (!tableRef || !scrollRef) {
+      return;
+    }
+
+    // only call scrollToItem if the list is actually scrollable (height of the
+    // content is bigger than it's container). Otherwise this might cause
+    // problems: https://github.com/bvaughn/react-window/issues/49
+    const isScrollable = tableRef.props.height < scrollRef.offsetHeight;
+
+    if (tableRef && this.props.rows.length > 1 && isScrollable) {
+      tableRef.scrollToItem(this.props.rows.length - 1);
     }
   }