fixup singleton guards

Author: Gankra

src/raw/mod.rs

@@ -649,10 +649,10 @@ impl<T> RawTable<T> {
     #[inline]
     pub fn clear_no_drop(&mut self) {
         unsafe {
-            if !self.is_empty_singleton() {
-                self.ctrl(0).write_bytes(EMPTY, self.num_ctrl_bytes());
+            if self.is_empty_singleton() {
+                return;
             }
-
+            self.ctrl(0).write_bytes(EMPTY, self.num_ctrl_bytes());
             let header = self.header_mut();
             header.items = 0;
             header.growth_left = bucket_mask_to_capacity(header.bucket_mask);
@@ -869,6 +869,11 @@ impl<T> RawTable<T> {
 
             // Allocate and initialize the new table.
             let mut new_table = Self::try_with_capacity(capacity, fallability)?;
+            if new_table.is_empty_singleton() {
+                mem::swap(self, &mut new_table);
+                return Ok(());
+            }
+
             let new_header = new_table.header_mut();
             new_header.growth_left -= self.items();
             new_header.items = self.items();