can't represent 65536 pages

[nlewycky]

Describe the bug

Memory minimum and maximum sizes range 0..65536 inclusive. The verifier blocks 65537 and higher. However, wasmer only works on 65535 and lower.

Testcase:

(module (memory (;0;) 65536))

fails:

$ target/release/wasmer --cranelift x.wat 
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: TryFromIntError(())', lib/vm/src/memory.rs:262:74
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The line of code in question is:

        let mem_length = memory.minimum.bytes().0.try_into().unwrap();

and the error is that 65536*65536 is 4294967296, which is the first value too large to fit in a u32.

Wasmer needs to either remove the problematic conversions to bytes keeping the value as pages, use a larger datatype for the byte count, or store it in a 'max-1' format (assuming '0' is unnecessary since we store the absence of a memory differently.)