Crash from attempting to display messages in one channel

[cleeyv]

Attempting to display the messages from one of my groups caused gurk to abort with the following errors:

memory allocation of 18446744073709551609 bytes failed
Thread 1 "gurk" received signal SIGABRT, Aborted.
0x00007ffff7c80d22 in raise () from /usr/lib/libc.so.6

I got a backtrace from gdb and it looked like this:

(gdb) bt
#0  0x00007f1f06468d22 in raise () from /usr/lib/libc.so.6
#1  0x00007f1f06452862 in abort () from /usr/lib/libc.so.6
#2  0x0000562b51c0d98a in std::sys::unix::abort_internal () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/sys/unix/mod.rs:237
#3  0x0000562b51c009e9 in std::process::abort () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/process.rs:1792
#4  0x0000562b51c03d20 in std::alloc::rust_oom () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/alloc.rs:332
#5  0x0000562b51608f7a in alloc::alloc::__alloc_error_handler::__rg_oom () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/alloc.rs:397
#6  0x0000562b515f2187 in __rust_alloc_error_handler ()
#7  0x0000562b51608f69 in alloc::alloc::handle_alloc_error () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/alloc.rs:366
#8  0x0000562b516096d0 in alloc::raw_vec::RawVec::allocate_in<u8,alloc::alloc::Global> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/raw_vec.rs:206
#9  alloc::raw_vec::RawVec::with_capacity_in<u8,alloc::alloc::Global> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/raw_vec.rs:142
#10 alloc::vec::Vec::with_capacity_in<u8,alloc::alloc::Global> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/vec/mod.rs:574
#11 alloc::vec::Vec::with_capacity<u8> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/vec/mod.rs:440
#12 alloc::slice::{{impl}}::repeat<u8> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/slice.rs:534
#13 alloc::str::{{impl}}::repeat () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/alloc/src/str.rs:493
#14 0x0000562b517b211b in core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut ()
#15 0x0000562b51791e55 in <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::next ()
#16 0x0000562b517ab348 in <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter ()
#17 0x0000562b517c59f6 in gurk::ui::draw ()
#18 0x0000562b5174c2e6 in tui::terminal::Terminal<B>::draw ()
#19 0x0000562b5184b133 in gurk::run_single_threaded::_$u7b$$u7b$closure$u7d$$u7d$::hd2afcf3e81f1528e ()
#20 0x0000562b516ee9f6 in tokio::macros::scoped_tls::ScopedKey<T>::set ()
#21 0x0000562b518201f7 in <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll ()
#22 0x0000562b51727adc in tokio::runtime::enter::Enter::block_on ()
#23 0x0000562b517a378e in tokio::runtime::thread_pool::ThreadPool::block_on ()
#24 0x0000562b51862d2a in tokio::runtime::Runtime::block_on ()
#25 0x0000562b517c77d6 in gurk::main ()
#26 0x0000562b517b0c36 in std::sys_common::backtrace::__rust_begin_short_backtrace ()
#27 0x0000562b517b0c4d in std::rt::lang_start::{{closure}} ()
#28 0x0000562b51c05160 in core::ops::function::impls::{{impl}}::call_once<(),Fn<()>> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399/library/core/src/ops/function.rs:259
#29 std::panicking::try::do_call<&Fn<()>,i32> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/panicking.rs:379
#30 std::panicking::try<i32,&Fn<()>> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/panicking.rs:343
#31 std::panic::catch_unwind<&Fn<()>,i32> () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/panic.rs:431
#32 std::rt::lang_start_internal () at /rustc/a143517d44cac50b20cbd3a0b579addab40dd399//library/std/src/rt.rs:51
#33 0x0000562b517c78b5 in main ()

Based on lines 15-18, I assumed that the issue somewhere in fn draw_messages in ui.rs.

When I built it locally, the --verbose log showed the following error:

[2021-07-18T14:52:11.760959272-04:00 ERROR log_panics] thread 'main' panicked at 'attempt to subtract with overflow': src/ui.rs:300

This was enough info for PR that seems to have fixed the problem.