fix: NonEmpty::capacity returns NonZeroUsize

Author: FintanH

CHANGELOG.md

@@ -5,6 +5,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this library adheres to Rust's notion of
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.12.0
+- `NonEmpty::capacity` returns `NonZeroUsize`
+
 ## 0.11.0
 
 ### Added

src/lib.rs

@@ -349,8 +349,8 @@ impl<T> NonEmpty<T> {
     }
 
     /// Get the capacity of the list.
-    pub fn capacity(&self) -> usize {
-        self.tail.capacity() + 1
+    pub fn capacity(&self) -> NonZeroUsize {
+        NonZeroUsize::MIN.saturating_add(self.tail.capacity())
     }
 
     /// Get the last element. Never fails.