Fix OnceCell::take not reverting the inner state

This would result in a panic from an unwrap when attempting to
re-initialize the cell.

src/lib.rs

@@ -515,6 +515,7 @@ impl<T> OnceCell<T> {
 
     /// Takes the value out of this `OnceCell`, moving it back to an uninitialized state.
     pub fn take(&mut self) -> Option<T> {
+        self.inner = Inner::new();
         self.value.get_mut().take()
     }