added rangeCount check. see facebookarchive#1571

Author: zackham

src/component/selection/setDraftEditorSelection.js

@@ -304,9 +304,11 @@ function addFocusToSelection(
     // Additionally, clone the selection range. IE11 throws an
     // InvalidStateError when attempting to access selection properties
     // after the range is detached.
-    var range = selection.getRangeAt(0);
-    range.setEnd(node, offset);
-    selection.addRange(range.cloneRange());
+    if (selection.rangeCount > 0) {
+      var range = selection.getRangeAt(0);
+      range.setEnd(node, offset);
+      selection.addRange(range.cloneRange());
+    }
   }
 }