Generate method body when there is no body for the method

Problem: when using a stubbed API jar such as the Java EE API jar, where the methods have no bodies at all, Soot will be unable to handle those and crash with an exception like this: `java.lang.RuntimeException: Unable to load the body for method <javax.servlet.GenericServlet: void <clinit>()>`

Solution: when a method has no body create a fake body that will allow Soot to move on.