fix inspect and explore panics on empty records (#13893)

# Description

Fixes a couple panics:

```
> {} | inspect
Error:   x Main thread panicked.
  |-> at crates/nu-command/src/debug/inspect_table.rs:87:15
  `-> attempt to divide by zero
```

```
> {} | explore
# see an empty column, press Down
Error:   x Main thread panicked.
  |-> at crates/nu-explore/src/views/cursor/mod.rs:39:9
  `-> attempt to subtract with overflow
```

# User-Facing Changes

`{} | inspect` now outputs an empty table:

```
╭─────────────┬────────╮
│ description │ record │
├─────────────┴────────┤
│                      │
├──────────────────────┤
```

`{} | explore` opens the help menu.

Both match the empty list behavior.

# Tests

I'm not sure how to test `explore`, as it waits for interaction.

crates/nu-explore/src/nu_common/value.rs

@@ -92,8 +92,15 @@ pub fn collect_input(value: Value) -> Result<(Vec<String>, Vec<Vec<Value>>)> {
     let span = value.span();
     match value {
         Value::Record { val: record, .. } => {
-            let (key, val) = record.into_owned().into_iter().unzip();
-            Ok((key, vec![val]))
+            let (key, val): (_, Vec<Value>) = record.into_owned().into_iter().unzip();
+
+            Ok((
+                key,
+                match val.is_empty() {
+                    true => vec![],
+                    false => vec![val],
+                },
+            ))
         }
         Value::List { vals, .. } => {
             let mut columns = get_columns(&vals);