flac: fix issues reported by errcheck and unconvert

enc.go:178:35: unnecessary conversion (unconvert)
	if err := enc.bw.WriteBits(uint64(si.NSamples), 36); err != nil {
	                                 ^
enc.go:543:34: unnecessary conversion (unconvert)
	if _, err := enc.bw.Write([]byte(pic.Data)); err != nil {
	                                ^

frame/frame.go:161:17: Error return value of `md5sum.Write` is not checked (errcheck)
				md5sum.Write(buf[:1])
				            ^
frame/frame.go:165:17: Error return value of `md5sum.Write` is not checked (errcheck)
				md5sum.Write(buf[:2])
				            ^
frame/frame.go:170:17: Error return value of `md5sum.Write` is not checked (errcheck)
				md5sum.Write(buf[:])
				            ^

Updates #25.

.travis.yml

@@ -26,4 +26,4 @@ before_script:
 
 script:
   - ./goclean.sh
-  - golangci-lint run
+  - golangci-lint run --enable-all

enc.go

@@ -175,7 +175,7 @@ func (enc *encoder) writeStreamInfo(hdr meta.Header, si *meta.StreamInfo) error
 	}
 
 	// 36 bits: NSamples.
-	if err := enc.bw.WriteBits(uint64(si.NSamples), 36); err != nil {
+	if err := enc.bw.WriteBits(si.NSamples, 36); err != nil {
 		return errutil.Err(err)
 	}
 
@@ -540,7 +540,7 @@ func (enc *encoder) writePicture(hdr meta.Header, pic *meta.Picture) error {
 	}
 
 	// (data length) bytes: Data.
-	if _, err := enc.bw.Write([]byte(pic.Data)); err != nil {
+	if _, err := enc.bw.Write(pic.Data); err != nil {
 		return errutil.Err(err)
 	}
 

frame/frame.go

@@ -158,16 +158,16 @@ func (frame *Frame) Hash(md5sum hash.Hash) {
 			switch bps {
 			case 8:
 				buf[0] = uint8(sample)
-				md5sum.Write(buf[:1])
+				_, _ = md5sum.Write(buf[:1])
 			case 16:
 				buf[0] = uint8(sample)
 				buf[1] = uint8(sample >> 8)
-				md5sum.Write(buf[:2])
+				_, _ = md5sum.Write(buf[:2])
 			case 24:
 				buf[0] = uint8(sample)
 				buf[1] = uint8(sample >> 8)
 				buf[2] = uint8(sample >> 16)
-				md5sum.Write(buf[:])
+				_, _ = md5sum.Write(buf[:])
 			default:
 				log.Printf("frame.Frame.Hash: support for %d-bit sample size not yet implemented", bps)
 			}