fix ability to disable block checksumming (#55)

* fix to disable block checksumming

Author: pmarks

src/encoder.rs

@@ -39,7 +39,7 @@ impl EncoderBuilder {
             block_size: BlockSize::Default,
             block_mode: BlockMode::Linked,
             checksum: ContentChecksum::ChecksumEnabled,
-            block_checksum: BlockChecksum::NoBlockChecksum,
+            block_checksum: BlockChecksum::BlockChecksumEnabled,
             level: 0,
             auto_flush: false,
             favor_dec_speed: false,
@@ -99,7 +99,7 @@ impl EncoderBuilder {
                 content_size: self.content_size.clone(),
                 frame_type: FrameType::Frame,
                 dict_id: 0,
-                block_checksum_flag: BlockChecksum::BlockChecksumEnabled,
+                block_checksum_flag: self.block_checksum.clone(),
             },
             compression_level: self.level,
             auto_flush: if self.auto_flush { 1 } else { 0 },