Fix UB in offset calculation

Author: sfackler

src/lib.rs

@@ -28,7 +28,10 @@ extern "C" {
 
 fn sun_path_offset() -> usize {
     unsafe {
-        &(*(0 as *const libc::sockaddr_un)).sun_path as *const _ as usize
+        let addr: libc::sockaddr_un = mem::zeroed();
+        let base = &addr as *const _ as usize;
+        let path = &addr.sun_path as *const _ as usize;
+        path - base
     }
 }