Shared: Add CFG consistency check for scopes with missing entry points

shared/controlflow/codeql/controlflow/Cfg.qll

@@ -1387,9 +1387,13 @@ module Make<LocationSig Location, InputSig<Location> Input> {
       strictcount(sk.getListOrder()) > 1
     }
 
+    /** Holds if `n` has multiple textual representations. */
     query predicate multipleToString(Node n, string s) {
       s = strictconcat(n.toString(), ",") and
       strictcount(n.toString()) > 1
     }
+
+    /** Holds if CFG scope `scope` lacks an initial AST node. */
+    query predicate scopeNoFirst(CfgScope scope) { not scopeFirst(scope, _) }
   }
 }