hello_compute: check for missing command-line args (#4939)

* hello_compute: check for missing command-line args

Fixes off-by-one error when checking for missing arguments.
Before this, running the example gave this scary looking error message:

```
$ cargo run --bin wgpu-examples hello_compute
    Finished dev [unoptimized + debuginfo] target(s) in 0.13s
     Running `target/debug/wgpu-examples hello_compute`
[2023-12-27T22:14:26Z ERROR wgpu::backend::direct] Handling wgpu errors as fatal by default
thread 'main' panicked at 'wgpu error: Validation Error

Caused by:
    In Device::create_bind_group
    Buffer binding size 0 is less than minimum 4
      note: buffer = `Storage Buffer`

', wgpu/src/backend/direct.rs:3139:5
```

As this was the first example I tried to run, it almost scared me
away, thinking it was a driver issue.

Instead, without arguments the example should use defaults.

* Add PR #4939 to changelog as instructed

CHANGELOG.md

@@ -217,6 +217,7 @@ Passing an owned value `window` to `Surface` will return a `Surface<'static>`. S
 ### Examples
 
 - remove winit dependency from hello-compute example by @psvri in [#4699](https://github.com/gfx-rs/wgpu/pull/4699)
+- hello-compute example fix failure with "wgpu error: Validation Error" if arguments are missing by @vilcans in [#4939](https://github.com/gfx-rs/wgpu/pull/4939)
 - Made the examples page not crash on Chrome on Android, and responsive to screen sizes by @Dinnerbone in [#4958](https://github.com/gfx-rs/wgpu/pull/4958)
 
 ## v0.18.1 (2023-11-15)

examples/src/hello_compute/mod.rs

@@ -6,7 +6,7 @@ const OVERFLOW: u32 = 0xffffffff;
 
 #[cfg_attr(test, allow(dead_code))]
 async fn run() {
-    let numbers = if std::env::args().len() <= 1 {
+    let numbers = if std::env::args().len() <= 2 {
         let default = vec![1, 2, 3, 4];
         println!("No numbers were provided, defaulting to {default:?}");
         default