fix explicit constructor in copy-initialization (#6884)
fix explicit constructor in copy-initialization (#6884)

commit: https://github.com/envoyproxy/envoy/commit/4c80194bf82193261aa52a4ca64c4e6a461881c0#diff-5d52e6425da0cdb53f84da8906c0a968R602
happened to break our builds because of it's use of `return {}`'s
it introduced into upstream_impl.cc (we use a toolchain built around
clang-9, to more accurately map with the rest of our tools). this
fixes that build error.

Risk Level: Low
Docs Changes: N/A
Release Notes: N/A

Signed-off-by: Eric <e4674042a0b1aef8cb92a5ded6745c5cf4620423@rust-lang.life>

istio/envoy,jrajahalme/envoy,envoyproxy/envoy,lyft/envoy,istio/envoy,eklitzke/envoy,lyft/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy-wasm,istio/envoy,envoyproxy/envoy,lyft/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,eklitzke/envoy,envoyproxy/envoy,jrajahalme/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,istio/envoy,jrajahalme/envoy,eklitzke/envoy,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,lizan/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy,lyft/envoy,eklitzke/envoy,envoyproxy/envoy,lizan/envoy,lizan/envoy,eklitzke/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,jrajahalme/envoy