Fixes #1427: Prints help message with -h switch (#1454)

For some commands like `which` -h flag would trigger an error asking for
missing required parameters instead of printing the help message as it
does with --help. This commit adds a check in the command parser to
avoid that.

crates/nu-parser/src/hir.rs

@@ -74,11 +74,7 @@ impl Call {
     pub fn switch_preset(&self, switch: &str) -> bool {
         self.named
             .as_ref()
-            .and_then(|n| n.get(switch))
-            .map(|t| match t {
-                NamedValue::PresentSwitch(_) => true,
-                _ => false,
-            })
+            .map(|n| n.switch_present(switch))
             .unwrap_or(false)
     }
 }