CFG: Exclude blocks from post-order in case they're Exprs.

Author: aschackmull

shared/controlflow/codeql/controlflow/ControlFlowGraph.qll

@@ -571,7 +571,8 @@ module Make0<LocationSig Location, AstSig<Location> Ast> {
       not n instanceof LogicalNotExpr and
       not n instanceof ConditionalExpr and
       not n instanceof Switch and
-      not n instanceof Case
+      not n instanceof Case and
+      not n instanceof BlockStmt
     }
 
     /**