[ASTMatchers] Fix matching after generic top-level matcher

With a matcher like

  expr(anyOf(integerLiteral(equals(42)), unless(expr())))

and code such as

  struct B {
    B(int);
  };

  B func1() { return 42; }

the top-level expr() would match each of the nodes which are not spelled
in the source and then ignore-traverse to match the integerLiteral node.
This would result in multiple results reported for the integerLiteral.

Fix that by only running matching logic on nodes which are not skipped
with the top-level matcher.

Differential Revision: https://reviews.llvm.org/D95735

(cherry picked from commit d6a06365)