Java: Make loop classes extend LoopStmt and use getBody instead of getStmt.

java/ql/src/Likely Bugs/Termination/SpinOnField.ql

@@ -37,12 +37,12 @@ class EmptyLoop extends Stmt {
     exists(ForStmt stmt | stmt = this |
       not exists(stmt.getAnInit()) and
       not exists(stmt.getAnUpdate()) and
-      stmt.getStmt() instanceof Empty
+      stmt.getBody() instanceof Empty
     )
     or
-    this.(WhileStmt).getStmt() instanceof Empty
+    this.(WhileStmt).getBody() instanceof Empty
     or
-    this.(DoStmt).getStmt() instanceof Empty
+    this.(DoStmt).getBody() instanceof Empty
   }
 
   Expr getCondition() {