Fix #23 return early if not called on a object

Author: lukeapage

lib/rules/no-assigning-return-values.js

@@ -35,6 +35,9 @@ function isCypressCommandDeclaration(declarator) {
   if (!declarator.init.callee) { return; }
 
   let object = declarator.init.callee.object;
+
+  if (!object)                 { return; }
+
   while (object.callee) {
     object = object.callee.object;
   }