logname: reduce range of unsafe block

Author: oech3

src/uu/logname/src/logname.rs

@@ -12,13 +12,11 @@ use uucore::translate;
 use uucore::{error::UResult, show_error};
 
 fn get_userlogin() -> Option<String> {
-    unsafe {
-        let login: *const libc::c_char = libc::getlogin();
-        if login.is_null() {
-            None
-        } else {
-            Some(String::from_utf8_lossy(CStr::from_ptr(login).to_bytes()).to_string())
-        }
+    let login_ptr = unsafe { libc::getlogin() };
+    if login_ptr.is_null() {
+        None
+    } else {
+        Some(String::from_utf8_lossy(unsafe { CStr::from_ptr(login_ptr) }.to_bytes()).to_string())
     }
 }