Deal with invalid UTF-8 from gai_strerror

When the system is using a non-UTF-8 locale, the value will indeed not
be UTF-8. That sucks for everyone involved, but is no reason for panic.
We can "handle" this gracefully by just using from lossy, replacing the
invalid UTF-8 with the ? and keeping the accidentally valid UTF-8.
Good luck when debugging, but at least it's not a crash.

We already do this for `strerror_r`.

std/src/sys/pal/unix/net.rs

@@ -4,7 +4,6 @@ use crate::io::{self, BorrowedBuf, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem;
 use crate::net::{Shutdown, SocketAddr};
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, RawFd};
-use crate::str;
 use crate::sys::fd::FileDesc;
 use crate::sys::pal::unix::IsMinusOne;
 use crate::sys_common::net::{getsockopt, setsockopt, sockaddr_to_addr};
@@ -47,7 +46,9 @@ pub fn cvt_gai(err: c_int) -> io::Result<()> {
 
     #[cfg(not(target_os = "espidf"))]
     let detail = unsafe {
-        str::from_utf8(CStr::from_ptr(libc::gai_strerror(err)).to_bytes()).unwrap().to_owned()
+        // We can't always expect a UTF-8 environment. When we don't get that luxury,
+        // it's better to give a low-quality error message than none at all.
+        CStr::from_ptr(libc::gai_strerror(err)).to_string_lossy()
     };
 
     #[cfg(target_os = "espidf")]