don't panic on mapped buffer in queue_submit (#3364)

CHANGELOG.md

@@ -182,6 +182,7 @@ Additionally `Surface::get_default_config` now returns an Option and returns Non
 - Improve error messages when binding bind group with dynamic offsets. By @cwfitzgerald in [#3294](https://github.com/gfx-rs/wgpu/pull/3294)
 - Allow non-filtering sampling of integer textures. By @JMS55 in [#3362](https://github.com/gfx-rs/wgpu/pull/3362).
 - Validate texture ids in `Global::queue_texture_write`. By @jimblandy in [#3378](https://github.com/gfx-rs/wgpu/pull/3378).
+- Don't panic on mapped buffer in queue_submit. By @crowlKats in [#3364](https://github.com/gfx-rs/wgpu/pull/3364).
 
 #### Metal
 - Fix texture view creation with full-resource views when using an explicit `mip_level_count` or `array_layer_count`. By @cwfitzgerald in [#3323](https://github.com/gfx-rs/wgpu/pull/3323)

wgpu-core/src/device/queue.rs

@@ -307,6 +307,8 @@ pub enum QueueSubmitError {
     DestroyedTexture(id::TextureId),
     #[error(transparent)]
     Unmap(#[from] BufferAccessError),
+    #[error("Buffer {0:?} is still mapped")]
+    BufferStillMapped(id::BufferId),
     #[error("surface output was dropped before the command buffer got submitted")]
     SurfaceOutputDropped,
     #[error("surface was unconfigured before the command buffer got submitted")]
@@ -910,7 +912,7 @@ impl<G: GlobalIdentityHandlerFactory> Global<G> {
                             } else {
                                 match buffer.map_state {
                                     BufferMapState::Idle => (),
-                                    _ => panic!("Buffer {:?} is still mapped", id),
+                                    _ => return Err(QueueSubmitError::BufferStillMapped(id.0)),
                                 }
                             }
                         }