Server crashes when connected to from multiple clients under certain conditions

[Casey Primozic]

[tectonic-1]2018-03-31T04:56:04.448768213Z [2018-03-31][04:5604:448603709][tectonic_server::plugins::gstorage::run][INFO] Need to upload 0 files.
[tectonic-1]2018-03-31T04:56:04.861235932Z [2018-03-1][04:56:04:861008880][tectonic_server::server][INFO] Client connected. Current: 2.
[tectonic-1]2018-03-31T04:56:04.864033967Z thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', libcore/option.rs:335:21
[tectonic-1]2018-03-31T04:56:05.189609879Z stack backtrace:
[tectonic-1]2018-03-31T04:56:05.189687246Z    0:std::sys::unix::backtrace::tracing::imp::unwind_backtrace
[tectonic-1]2018-03-31T04:56:05.203499788Z              at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
[tectonic-1]2018-03-31T04:56:05.203560268Z    1: std::sys_common::backtrace::print
[tectonic-1]2018-03-31T04:56:05.205063950Z              at libstd/sys_common/backtrace.rs:71
[tectonic-1]2018-03-31T04:56:05.205087479Z              at libstd/sys_common/backtrace.rs:59
[tectonic-1]2018-03-31T04:56:05.205096772Z    2: std::panicking::default_hook::{{closure}}
[tectonic-1]2018-03-31T04:56:05.207197720Z              at libstd/panicking.rs:207
[tectonic-1]2018-03-31T04:56:05.207217797Z    3: std::panicking::default_hook
[tectonic-1]2018-03-31T04:56:05.207236221Z              at libstd/panicking.rs:223
[tectonic-1]2018-03-31T04:56:05.207250501Z    4: std::panicking::rust_panic_with_hook
[tectonic-1]2018-03-31T04:56:05.207255778Z              at libstd/panicking.rs:402
[tectonic-1]2018-03-31T04:56:05.207285279Z    5: std::panicking::begin_panic_fmt
[tectonic-1]2018-03-31T04:56:05.207294583Z              at libstd/panicking.rs:349
[tectonic-1]2018-03-31T04:56:05.207299475Z    6: rust_begin_unwind
[tectonic-1]2018-03-31T04:56:05.207304360Z              at libstd/panicking.rs:325
[tectonic-1]2018-03-31T04:56:05.207309087Z    7: core::panicking::panic_fmt
[tectonic-1]2018-03-31T04:56:05.209775588Z              at libcore/panicking.rs:72
[tectonic-1]2018-03-31T04:56:05.209795418Z    8: core::panicking::panic
[tectonic-1]2018-03-31T04:56:05.209802357Z              at libcore/panicking.rs:51
[tectonic-1]2018-03-31T04:56:05.209807435Z    9: tectonic_server::handler::gen_response
[tectonic-1]2018-03-31T04:56:05.209819673Z   10: <futures::stream::fold::Fold<S, F, Fut, T> as futures::future::Future>::poll
[tectonic-1]2018-03-31T04:56:05.209835370Z   11: <futures::future::chain::Chain<A, B, C>>::poll
[tectonic-1]2018-03-31T04:56:05.209844951Z   12: futures::task_impl::std::set
[tectonic-1]2018-03-31T04:56:05.209856753Z   13:tokio::executor::current_thread::CurrentRunner::set_spawn
[tectonic-1]2018-03-31T04:56:05.209890861Z   14:<tokio::executor::current_thread::scheduler::Scheduler<U>>::tick
[tectonic-1]2018-03-31T04:56:05.209905963Z   15: <scoped_tls::ScopedKey<T>>::set
[tectonic-1]2018-03-31T04:56:05.209934525Z   16: <std::thread::local::LocalKey<T>>::with
[tectonic-1]2018-03-31T04:56:05.209992676Z   17: <std::thread::local::LocalKey<T>>::with
[tectonic-1]2018-03-31T04:56:05.210003670Z   18: tokio_core::reactor::Core::poll
[tectonic-1]2018-03-31T04:56:05.210008512Z   19: tectonic_server::server::run_server
[tectonic-1]2018-03-31T04:56:05.210017277Z   20: tectonic_server::main
[tectonic-1]2018-03-31T04:56:05.210022304Z   21: std::rt::lang_start::{{closure}}
[tectonic-1]2018-03-31T04:56:05.210033606Z   22: std::panicking::try::do_call
[tectonic-1]2018-03-31T04:56:05.210078849Z              at libstd/rt.rs:59
[tectonic-1]2018-03-31T04:56:05.210094392Z              at libstd/panicking.rs:306
[tectonic-1]2018-03-31T04:56:05.210100069Z   23: __rust_maybe_catch_panic
[tectonic-1]2018-03-31T04:56:05.210380609Z              at libpanic_unwind/lib.rs:102
[tectonic-1]2018-03-31T04:56:05.210418051Z   24: std::rt::lang_start_internal
[tectonic-1]2018-03-31T04:56:05.210427495Z              at libstd/panicking.rs:285
[tectonic-1]2018-03-31T04:56:05.210432191Z              at libstd/panic.rs:361
[tectonic-1]2018-03-31T04:56:05.210436775Z              at libstd/rt.rs:58
[tectonic-1]2018-03-31T04:56:05.210442128Z   25: main