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-command/src/debug/inspect_table.rs

@@ -152,7 +152,7 @@ fn truncate_data(
     let left_space = expected_width - width;
     let has_space_for_truncation_column = left_space > PAD;
     if !has_space_for_truncation_column {
-        peak_count -= 1;
+        peak_count = peak_count.saturating_sub(1);
     }
 
     remove_columns(data, peak_count);
@@ -201,11 +201,18 @@ mod util {
             Value::Record { val: record, .. } => {
                 let (cols, vals): (Vec<_>, Vec<_>) = record.into_owned().into_iter().unzip();
                 (
-                    cols,
+                    match cols.is_empty() {
-                    vec![vals
+                        true => vec![String::from("")],
+                        false => cols,
+                    },
+                    match vals
                         .into_iter()
                         .map(|s| debug_string_without_formatting(&s))
-                        .collect()],
+                        .collect::<Vec<String>>()
+                    {
+                        vals if vals.is_empty() => vec![],
+                        vals => vec![vals],
+                    },
                 )
             }
             Value::List { vals, .. } => {

crates/nu-command/tests/commands/inspect.rs

@@ -5,3 +5,15 @@ fn inspect_with_empty_pipeline() {
     let actual = nu!("inspect");
     assert!(actual.err.contains("no input value was piped in"));
 }
+
+#[test]
+fn inspect_with_empty_list() {
+    let actual = nu!("[] | inspect");
+    assert!(actual.out.contains("empty list"));
+}
+
+#[test]
+fn inspect_with_empty_record() {
+    let actual = nu!("{} | inspect");
+    assert!(actual.out.contains("empty record"));
+}

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();
+            let (key, val): (_, Vec<Value>) = record.into_owned().into_iter().unzip();
-            Ok((key, vec![val]))
+
+            Ok((
+                key,
+                match val.is_empty() {
+                    true => vec![],
+                    false => vec![val],
+                },
+            ))
         }
         Value::List { vals, .. } => {
             let mut columns = get_columns(&vals);