Calling .vstack() on empty dataframe results in wrong shape

[letkemann]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

use polars::prelude::*;

fn main() {
    let df_empty = DataFrame::empty();
    let df_data = df!("data" => [1, 2, 3]).unwrap();
    let df = df_empty.vstack(&df_data).unwrap();

    println!("Shape: {:?}", df.shape()); // Shape: (0, 1)
    println!("{df}"); // panic
}

Log output

Shape: (0, 1)
thread 'main' panicked at /home/user/.cargo/registry/src/index.crates.io-6f17d22bba15001f/polars-core-0.44.2/src/fmt.rs:567:13:
The column lengths in the DataFrame are not equal.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Issue description

The height of the 'data' dataframe is not copied to the empty dataframe. This results in panic when trying to print the dataframe.

Expected behavior

The empty dataframe should take over the shape of the 'data' dataframe.
Output polars version 0.43.1:

shape: (3, 1)
┌──────┐
│ data │
│ ---  │
│ i32  │
╞══════╡
│ 1    │
│ 2    │
│ 3    │
└──────┘

### Installed versions

polars = { version = "0.44.2" }