io/region: allow stopping foreach_chunk early

Errors returned from the callback stop the loop early.

src/bin/regiondump.rs

@@ -15,6 +15,7 @@ fn main() -> Result<()> {
 	minedmap::io::region::from_file(args.file.as_path())?.foreach_chunk(
 		|coords, value: fastnbt::Value| {
 			println!("Chunk {:?}: {:#x?}", coords, value);
+			Ok(())
 		},
 	)
 }

src/io/region.rs

@@ -73,7 +73,7 @@ impl<R: Read + Seek> Region<R> {
 	where
 		R: Read + Seek,
 		T: DeserializeOwned,
-		F: FnMut(ChunkCoords, T),
+		F: FnMut(ChunkCoords, T) -> Result<()>,
 	{
 		let Region { mut reader } = self;
 
@@ -119,7 +119,7 @@ impl<R: Read + Seek> Region<R> {
 			let chunk = decode_chunk(&buffer)
 				.with_context(|| format!("Failed to decode data for chunk {:?}", coords))?;
 
-			f(coords, chunk);
+			f(coords, chunk)?;
 		}
 
 		Ok(())

src/main.rs

@@ -41,14 +41,15 @@ impl RegionProcessor {
 				Ok(chunk) => chunk,
 				Err(err) => {
 					eprintln!("Chunk {:?}: {}", coords, err);
-					return;
+					return Ok(());
 				}
 			};
 
 			match world::layer::top_layer(&chunk, &self.block_types) {
 				Ok(_) => {}
 				Err(err) => println!("{:?}", err),
-			}
+			};
+			Ok(())
 		})
 	}