SslMeterBinder doesn't register metrics for dynamically added bundles if no bundles exist at bind time

[mhalbritter]

This test (added to org.springframework.boot.actuate.autoconfigure.ssl.SslMeterBinderTests) shouldn't fail:

@Test
void test() {
	DefaultSslBundleRegistry sslBundleRegistry = new DefaultSslBundleRegistry();
	MeterRegistry meterRegistry = bindToRegistry(sslBundleRegistry);
	sslBundleRegistry.registerBundle("dummy", SslBundle.of(createSslStoreBundle("classpath:test.p12")));
	assertThat(meterRegistry.getMeters()).isNotEmpty();
}