fix moonfire_ffmpeg::Error formatting
This would return a string with trailing nuls up to the buffer size (64
bytes) which would cause problems later. One in particular: in
"moonfire-nvr config", if testing a camera failed, displaying the error would
panic with the backtrace below.
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: NulError(33, [69, 114, 114, 111, 114, 58, 32, 102, 102, 109, 112, 101, 103, 58, 32, 67, 111, 110, 110, 101, 99, 116, 105, 111, 110, 32, 114, 101, 102, 117, 115, 101, 100, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])', src/libcore/result.rs:860:4
stack backtrace:
0: std::sys:👿:backtrace::tracing:👿:unwind_backtrace
1: std::panicking::default_hook::{{closure}}
2: std::panicking::default_hook
3: std::panicking::rust_panic_with_hook
4: std::panicking::begin_panic_new
5: std::panicking::begin_panic_fmt
6: rust_begin_unwind
7: core::panicking::panic_fmt
8: core::result::unwrap_failed
9: <core::result::Result<T, E>>::unwrap
10: <&'a str as ncurses::ToCStr>::to_c_str
11: ncurses::addstr
12: ncurses::mvaddstr
13: <cursive::backend::curses::n::Concrete as cursive::backend::Backend>::print_at
14: cursive:🖨️:Printer::print
15: <cursive::views::text_view::TextView as cursive::view::View>::draw::{{closure}}
16: cursive::view:📜:ScrollBase::draw
17: <cursive::views::text_view::TextView as cursive::view::View>::draw
18: <cursive::views::dialog::Dialog as cursive::view::View>::draw
19: <cursive::views::layer::Layer<T> as cursive::view::view_wrapper::ViewWrapper>::wrap_draw
20: cursive::view::view_wrapper::<impl cursive::view::View for T>::draw
21: <cursive::views::shadow_view::ShadowView<T> as cursive::view::view_wrapper::ViewWrapper>::wrap_draw
22: cursive::view::view_wrapper::<impl cursive::view::View for T>::draw
23: <cursive::views::stack_view::StackView as cursive::view::View>::draw::{{closure}}
24: cursive:🖨️:Printer::with_color::{{closure}}
25: <cursive::backend::curses::n::Concrete as cursive::backend::Backend>::with_color
26: cursive:🖨️:Printer::with_color
27: <cursive::views::stack_view::StackView as cursive::view::View>::draw
28: cursive::Cursive::draw
29: cursive::Cursive::step
30: cursive::Cursive::run
31: moonfire_nvr::cmds::config::run
32: moonfire_nvr::cmds::Command::run
33: moonfire_nvr::main
34: __rust_maybe_catch_panic
35: std::rt::lang_start
36: main
45b508dff6