Simplify Clone by removing redundant guards

[JustForFun88]

These extra guards only complicate the code where it is not needed anyway. The Drop function checks the number of items in a table before dropping elements (see below), so that dropping the uninitialize table as well as table with no actual data (but with FULL control bytes) is safe . Added tests to check that the current behavior of Drop won't change in the future.

impl<T, A: Allocator + Clone> Drop for RawTable<T, A> {
    fn drop(&mut self) {
        if !self.table.is_empty_singleton() {
            unsafe {
                self.drop_elements();
                self.free_buckets();
            }
        }
    }
}

impl<T, A: Allocator + Clone> RawTable<T, A> {
    unsafe fn drop_elements(&mut self) {
        if Self::DATA_NEEDS_DROP && !self.is_empty() {
            for item in self.iter() {
                item.drop();
            }
        }
    }
}

[JustForFun88]

By the way, the old implementation with ManuallyDrop seems to be leaking the allocator. I'll add a test later

The old implementation with ManuallyDrop actually leaked the allocator. A trifle of course, but still corrected the test to take this into account too.

[Amanieu]

@bors r+

[bors]

📌 Commit 50a9e7b has been approved by Amanieu

It is now in the queue for this repository.

[bors]

⌛ Testing commit 50a9e7b with merge bb6521e...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing bb6521e to master...