Fixed last command crash

When the last command has an input value larger than the data its
operating on it would crash.  Added a check to ensure there are enough
elements to take.

src/commands/last.rs

@@ -38,11 +38,14 @@ fn last(
 ) -> Result<OutputStream, ShellError> {
     let stream = async_stream! {
         let v: Vec<_> = context.input.into_vec().await;
-        let k = v.len() - (*amount as usize);
+        let count = (*amount as usize);
+        if count < v.len() {
+            let k = v.len() - count;
             for x in v[k..].iter() {
                 let y: Tagged<Value> = x.clone();
                 yield ReturnSuccess::value(y)
             }
+        }
     };
     Ok(stream.to_output_stream())
 }