JS: Add back CallReceiverStep() restriction

This was initially lost after rebasing with indentation changes

Author: asgerf

javascript/ql/lib/semmle/javascript/ApiGraphs.qll

@@ -1413,7 +1413,9 @@ module API {
         exists(DataFlow::TypeBackTracker t, StepSummary summary, DataFlow::Node next |
           next = trackDefNode(nd, t) and
           StepSummary::step(prev, next, summary) and
-          result = t.prepend(summary)
+          result = t.prepend(summary) and
+          // Block argument-passing into 'this' when it determines the call target
+          not summary = CallReceiverStep()
         )
       }