unistd::getgrouplist: Simplify buffer resizing

Author: JayH5

src/unistd.rs

@@ -1055,9 +1055,8 @@ pub fn getgrouplist(user: &CString, group: Gid) -> Result<Vec<Gid>> {
                 return Err(Error::invalid_argument())
             }
 
-            // Trigger buffer resizing
-            unsafe { groups.set_len(cap) };
-            groups.reserve(ngroups as usize - cap);
+            // Reserve space for at least ngroups
+            groups.reserve(ngroups as usize);
 
             // Even if the buffer gets resized to bigger than ngroups_max,
             // don't ever ask for more than ngroups_max groups