Random crashes with SimpleTextOutput Protocol on VirtualBox

[imtsuki]

Lately, I am experiencing random crashes with uefi-rs running on VirtualBox while writing to stdout. The panic message is like the following:

Panic in /Users/tsuki/.cargo/registry/src/mirrors.ustc.edu.cn-61ef6e0cd06fb9b8/uefi-0.4.3/src/logger.rs at (59, 13):
ERROR: called `Result::unwrap()` on an `Err` value: Error

After investigation, it turns out the following code causes this problem:

uefi-rs/src/proto/console/text/output.rs

Lines 164 to 166 in 006c388

	self.output_string(text)
	.warning_as_error()
	.map_err(|_| fmt::Error)

Where the UEFI firmware shipped with VirtualBox will report EFI_DEVICE_ERROR when we're outputting too fast, probably, I'm not sure.

Personally I think this is not a fatal error and since there is no extra error message returned by output_string(), I'll submit a PR that ignores EFI_DEVICE_ERROR here.