Undefined behaviour in winmm backend

[barafael]

Here, a packet is filled by bytes from a message:

midir/src/backend/winmm/mod.rs

Lines 509 to 513 in db24d55

	let packet: u32 = 0;
	let ptr = &packet as *const u32 as *mut u8;
	for i in 0..nbytes {
	unsafe { *ptr.offset(i as isize) = message[i] };
	}

This is undefined behaviour, because the address of an immutable u32 is taken and cast to a *mut u8, which is then written to in an unsafe block.

I have fixes ready in #136 but these are part of a rather large patchset, so if you like I can send a small patch ahead, too.

[barafael]

Here's a playground which you can use with Miri to see that it's actually undefined behaviour: playground link

[Boddlnagg]

Sorry, I have somehow missed this PR! I will probably just merge #136 eventually (after #135 and a rebase), I don't think a separate PR is necessary.

[barafael]

OK. I just did this PR because I wasn't sure you wanted to have the large blob of changes in #136 .