[singlepass backend] panic when unwraping read_table result (BrTable opcode)

[pventuzelo]

Describe the bug

wasmer using the singlepass backend will panic when:

• Result of read_table is unwraped even if this result is an Error.

$ ./target/release/wasmer run --backend singlepass panic_unwrap_brtable_singlepass.wasm
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: BinaryReaderError { message: "Invalid var_u32", offset: 4 }', src/libcore/result.rs:1084:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

wasmer/lib/singlepass-backend/src/codegen_x64.rs

Lines 6451 to 6452 in d639748

	Operator::BrTable { ref table } => {
	let (targets, default_target) = table.read_table().unwrap();

Status of my environment

$ echo "`./target/release/wasmer -V` | `rustc -V` | `uname -m`"
wasmer 0.11.0 | rustc 1.38.0-nightly (2d1a551e1 2019-08-08) | x86_64

version: 71b342e

Steps to reproduce

Download panic_unwrap_brtable_singlepass.zip

$ unzip panic_unwrap_brtable_singlepass.zip
$ ./target/release/wasmer run --backend singlepass panic_unwrap_brtable_singlepass.wasm

Expected behavior

wasmer should return and propagate the Error using ?.

Actual behavior

$ ./target/release/wasmer run --backend singlepass panic_unwrap_brtable_singlepass.wasm
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: BinaryReaderError { message: "Invalid var_u32", offset: 4 }', src/libcore/result.rs:1084:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

Additional context

Once fixing patch #1052 applied,

$ ./target/release/wasmer run --backend singlepass panic_unwrap_brtable_singlepass.wasm 
Error: Can't compile module: InternalError { msg: "Codegen(\"CodegenError { message: \\\"BrTable read_table: BinaryReaderError { message: \\\\\\\"Invalid var_u32\\\\\\\", offset: 4 }\\\" }\")" }

[syrusakbary]

This issue should now be fixed on master. Closing :)