fix unstable test case UdpListenerImplTest.SendData (#9119)
fix unstable test case UdpListenerImplTest.SendData (#9119)

If Network::Test::readFromSocket() return error code 'Again', `data.addresses_.peer_`
is null, `data.addresses_.peer_->asString()` causes crash because it dereferences
a null pointer.

Signed-off-by: lhuang8 <e2e49c33c4f16cf7ae9a4716e9583745aa98bcfc@ebay.com>
envoyproxy/envoy,lyft/envoy,eklitzke/envoy,eklitzke/envoy,envoyproxy/envoy,eklitzke/envoy,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,istio/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lyft/envoy,jrajahalme/envoy,lyft/envoy,jrajahalme/envoy,envoyproxy/envoy,lyft/envoy,eklitzke/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,envoyproxy/envoy,istio/envoy,lizan/envoy,istio/envoy,jrajahalme/envoy,lizan/envoy,istio/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,eklitzke/envoy,lizan/envoy,lizan/envoy,lizan/envoy,eklitzke/envoy,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm