message: Improve error messages from feedback
diff: @@ -534,7 +534,11 @@ pub unsafe extern "C" fn wasmer_instance_context_memory(
  let memory: &Memory = &**memory;
  return Some(&*(Box::into_raw(Box::new(memory.clone())) as *const wasmer_memory_t));
  } else {
  - // TODO: set error
  + update_last_error(CApiError {
  + msg:
  + "Internal error: memory is imported but the list of imported memories is empty"
  + .to_string(),
  + });
  return None;
  }
  } else {
  @@ -550,14 +554,19 @@ pub unsafe extern "C" fn wasmer_instance_context_memory(
  {
  name
  } else {
  - // TODO: set error
  + update_last_error(CApiError {
  + msg: "Could not find an exported memory".to_string(),
  + });
  return None;
  };
  let memory = instance
  .instance
  .exports
  .get_memory(exported_memory_name)
  - .expect("Todo");
  + .expect(&format!(
  + "Module exports memory named `{}` but it's inaccessible",
  + &exported_memory_name
  + ));
  Some(&*(Box::into_raw(Box::new(memory.clone())) as *const wasmer_memory_t))
  }
  }
  