Cfg: Update fallsThrough default.

Author: aschackmull

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -165,8 +165,6 @@ private module Ast implements AstSig<Location> {
 
   class DefaultCase extends Case instanceof J::DefaultCase { }
 
-  predicate fallsThrough(Case c) { not c.(J::SwitchCase).isRule() }
-
   class ConditionalExpr = J::ConditionalExpr;
 
   class BinaryExpr = J::BinaryExpr;

shared/controlflow/codeql/controlflow/ControlFlowGraph.qll

@@ -261,7 +261,7 @@ signature module AstSig<LocationSig Location> {
    * Holds if this case can fall through to the next case if it is not
    * otherwise prevented with a `break` or similar.
    */
-  default predicate fallsThrough(Case c) { none() }
+  default predicate fallsThrough(Case c) { not exists(c.getBody()) }
 
   /** A ternary conditional expression. */
   class ConditionalExpr extends Expr {