grammar nit

Author: RalfJung

library/alloc/src/rc.rs

@@ -1860,7 +1860,7 @@ impl<T: ?Sized> Weak<T> {
         let offset = unsafe { data_offset(ptr) };
 
         // Reverse the offset to find the original RcBox.
-        // SAFETY: we use wrapping_offset here because the pointer may be dangling (iff T: Sized).
+        // SAFETY: we use wrapping_offset here because the pointer may be dangling (but only if T: Sized).
         let ptr = unsafe {
             set_data_ptr(ptr as *mut RcBox<T>, (ptr as *mut u8).wrapping_offset(-offset))
         };

library/alloc/src/sync.rs

@@ -1643,7 +1643,7 @@ impl<T: ?Sized> Weak<T> {
         let offset = unsafe { data_offset(ptr) };
 
         // Reverse the offset to find the original ArcInner.
-        // SAFETY: we use wrapping_offset here because the pointer may be dangling (iff T: Sized)
+        // SAFETY: we use wrapping_offset here because the pointer may be dangling (but only if T: Sized)
         let ptr = unsafe {
             set_data_ptr(ptr as *mut ArcInner<T>, (ptr as *mut u8).wrapping_offset(-offset))
         };