Do not panic on corrupted input file

[visanalexandru]

When trying to decode a corrupted felics file, dfelics panics.
This is the stack trace:

thread 'main' panicked at src/compression/parameter_selection.rs:72:9:
assertion failed: context <= self.max_context
stack backtrace:
0: rust_begin_unwind
1: core::panicking::panic_fmt
2: core::panicking::panic
3: felics::compression::parameter_selection::KEstimator::get_k
4: felics::compression::decompress_channel
5: felics::compression::<impl felics::compression::traits::CompressDecompress for image::buffer_::ImageBuffer<image::color::Rgb,alloc::vec::Vec>>::decompress_with_header
6: felics::compression::decompress_image
7: dfelics::main
note: Some details are omitted, run with RUST_BACKTRACE=full for a verbose backtrace.