Fix not all pending data getting processed when finishing

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bdflib"
-version = "0.3.1"
+version = "0.3.2"
 authors = ["trivernis <trivernis@gmail.com>"]
 edition = "2018"
 license-file = "LICENSE"

src/io.rs

@@ -181,6 +181,7 @@ impl BDFWriter {
     /// Flushes the buffered chunk data and the writer
     /// to finish the file.
     pub fn finish(&mut self) -> Result<(), Error> {
+        self.flush()?;
         self.thread_manager.drop_sender();
         self.thread_manager.wait();
         self.flush()?;