Multiple panics caused by malformed inputs

Multiple runtime panics can be triggerred by constructing malformed data structures or function arguments. I believe the API design can be improve the get rid of these problems.

Examples:

```rust
use brotli::enc::command::BrotliDistanceParams;
use brotli::enc::command::Command;

fn main() {
let mut command = Command::default();
command.dist_prefix_ = 1000;
let params = BrotliDistanceParams {
distance_postfix_bits: 40,
num_direct_distance_codes: 0,
alphabet_size: 0,
max_distance: 0,
};
let _ = brotli::enc::command::CommandRestoreDistanceCode(&command, ¶ms);
}
```

```rust
use brotli::enc::command::PrefixEncodeCopyDistance;

fn main() {
let mut code = 0;
let mut extra_bits = 0;
PrefixEncodeCopyDistance(100, 0, 100, &mut code, &mut extra_bits);
}
```

```rust
use brotli::enc::brotli_bit_stream::BrotliBuildAndStoreHuffmanTreeFast;
use brotli::enc::writer::StandardAlloc;
fn main() {
let mut alloc = StandardAlloc::default();
BrotliBuildAndStoreHuffmanTreeFast(
&mut alloc,
&[0],
0,
0,
&mut [0],
&mut [0],
&mut 99999,
&mut [0],
);
}
```

Start by reproducing the three Rust examples and inspect CommandRestoreDistanceCode, PrefixEncodeCopyDistance, and BrotliBuildAndStoreHuffmanTreeFast. Determine the intended behavior for malformed structures and arguments; done means these inputs no longer cause runtime panics and the API behavior is covered by tests.

Written by the indexing model from the issue text.