Fix confusing WTF surrogate safety docs

Author: teor2345

library/std/src/ffi/os_str.rs

@@ -594,9 +594,9 @@ impl OsString {
 /// The slice must be valid for the platform encoding (as described in
 /// [`OsStr::from_encoded_bytes_unchecked`]).
 ///
-/// This bypasses the encoding-dependent surrogate joining, so `self` must
-/// not end with a leading surrogate half and `other` must not start with
-/// with a trailing surrogate half.
+/// This bypasses the encoding-dependent surrogate joining, so either
+/// `self` must not end with a leading surrogate half, or `other` must not
+/// start with a trailing surrogate half.
 #[inline]
 pub(crate)unsafefnextend_from_slice_unchecked(&mutself,other:&[u8]){
 // SAFETY: Guaranteed by caller.

library/std/src/sys/os_str/wtf8.rs

@@ -215,9 +215,9 @@ impl Buf {
 /// The slice must be valid for the platform encoding (as described in
 /// [`Slice::from_encoded_bytes_unchecked`]).
 ///
-/// This bypasses the WTF-8 surrogate joining, so `self` must not end with a
-/// leading surrogate half and `other` must not start with with a trailing
-/// surrogate half.
+/// This bypasses the WTF-8 surrogate joining, so either `self` must not
+/// end with a leading surrogate half, or `other` must not start with a
+/// trailing surrogate half.
 #[inline]
 pubunsafefnextend_from_slice_unchecked(&mutself,other:&[u8]){
 self.inner.extend_from_slice(other);