Return a Result from parse_using_rust_protobuf (test util) instead of panicking
Return a Result from parse_using_rust_protobuf (test util) instead of panicking

This makes it easier to write test cases that assert parsing returns
an error, without resorting to a `#[should_panic]`.

stepancheg/rust-protobuf,stepancheg/rust-protobuf,stepancheg/rust-protobuf