use let-else syntax where possible (#8886)

# Description
this pr changes some `if-let`s to `let-else`s

# User-Facing Changes
none

crates/nu-engine/src/column.rs

@@ -5,14 +5,14 @@ pub fn get_columns<'a>(input: impl IntoIterator<Item = &'a Value>) -> Vec<String
     let mut columns = vec![];
 
     for item in input {
-        if let Value::Record { cols, .. } = item {
-            for col in cols {
-                if !columns.contains(col) {
-                    columns.push(col.to_string());
-                }
-            }
-        } else {
+        let Value::Record { cols, .. } = item else {
             return vec![];
+        };
+
+        for col in cols {
+            if !columns.contains(col) {
+                columns.push(col.to_string());
+            }
         }
     }