fix double window class registration (#8548)

Author: Azorlogh

CHANGELOG.md

@@ -171,6 +171,7 @@ By @SupaMaggie70Incorporated in [#8206](https://github.com/gfx-rs/wgpu/pull/8206
 #### GLES
 
 - Fix race when downloading texture from compute shader pass. By @SpeedCrash100 in [#8527](https://github.com/gfx-rs/wgpu/pull/8527)
+- Fix double window class registration when dynamic libraries are used. By @Azorlogh in [#8548](https://github.com/gfx-rs/wgpu/pull/8548)
 
 #### hal
 

wgpu-hal/src/gles/wgl.rs

@@ -281,6 +281,21 @@ fn create_global_window_class() -> Result<CString, crate::InstanceError> {
     let name = format!("wgpu Device Class {:x}\0", class_addr as usize);
     let name = CString::from_vec_with_nul(name.into_bytes()).unwrap();
 
+    // The window class may already be registered if we are a dynamic library that got
+    // unloaded & loaded back into the same process. If so, just skip creation.
+    let already_exists = unsafe {
+        let mut wc = mem::zeroed::<WindowsAndMessaging::WNDCLASSEXA>();
+        WindowsAndMessaging::GetClassInfoExA(
+            Some(instance.into()),
+            PCSTR(name.as_ptr().cast()),
+            &mut wc,
+        )
+        .is_ok()
+    };
+    if already_exists {
+        return Ok(name);
+    }
+
     // Use a wrapper function for compatibility with `windows-rs`.
     unsafe extern "system" fn wnd_proc(
         window: Foundation::HWND,