Changed Struts2ActionSupportClassFieldReadSource to be a FieldValueNode instead of a field read

Author: atorralba

java/ql/lib/semmle/code/java/dataflow/FlowSources.qll

@@ -143,11 +143,10 @@ private class GuiceRequestParameterSource extends RemoteFlowSource {
   override string getSourceType() { result = "Guice request parameter" }
 }
 
-private class Struts2ActionSupportClassFieldReadSource extends RemoteFlowSource {
-  Struts2ActionSupportClassFieldReadSource() {
-    exists(Struts2ActionSupportClass c |
-      c.getASetterMethod().getField() = this.asExpr().(FieldRead).getField()
-    )
+private class Struts2ActionSupportClassFieldSource extends RemoteFlowSource {
+  Struts2ActionSupportClassFieldSource() {
+    this.(DataFlow::FieldValueNode).getField() =
+      any(Struts2ActionSupportClass c).getASetterMethod().getField()
   }
 
   override string getSourceType() { result = "Struts2 ActionSupport field" }