Fix extra newline on empty lists when $env.config.table.show_empty is… (#14766)

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# Description
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I just noticed that #14758 adds an extra newline when
`$env.config.table.show_empty = false`. This PR makes sure the
placeholder text is non-empty before adding the newline.

Before #14758:
```nushell
$env.config.table.show_empty = false
print ([]) text
# => text
echo []
```

Before PR:
```nushell
$env.config.table.show_empty = false
print ([]) text
# =>
# => text
echo []
# => 
```

After PR:
```nushell
$env.config.table.show_empty = false
print ([]) text
# => text
echo []
```


# User-Facing Changes
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None, fix to #14758 which has not been included in a release

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N/A

crates/nu-command/src/viewers/table.rs

@@ -886,7 +886,10 @@ impl Iterator for PagingTableCreator {
                     &self.stack,
                 );
                 let mut bytes = result.into_bytes();
-                bytes.push(b'\n');
+                // Add extra newline if show_empty is enabled
+                if !bytes.is_empty() {
+                    bytes.push(b'\n');
+                }
                 Some(Ok(bytes))
             } else {
                 None