Ignore empty Transfer-Encoding headers

Don't default to chunked. If we have a Content-Length header we have a fixed body.

header.go

@@ -1839,7 +1839,7 @@ func (h *ResponseHeader) parseHeaders(buf []byte) (int, error) {
 				}
 			case 't':
 				if caseInsensitiveCompare(s.key, strTransferEncoding) {
-					if !bytes.Equal(s.value, strIdentity) {
+					if len(s.value) > 0 && !bytes.Equal(s.value, strIdentity) {
 						h.contentLength = -1
 						h.h = setArgBytes(h.h, strTransferEncoding, strChunked, argsHasValue)
 					}

http_test.go

@@ -16,6 +16,22 @@ import (
 	"github.com/valyala/bytebufferpool"
 )
 
+func TestResponseEmptyTransferEncoding(t *testing.T) {
+	t.Parallel()
+
+	var r Response
+
+	body := "Some body"
+	br := bufio.NewReader(bytes.NewBufferString("HTTP/1.1 200 OK\r\nContent-Type: aaa\r\nTransfer-Encoding: \r\nContent-Length: 9\r\n\r\n" + body))
+	err := r.Read(br)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := string(r.Body()); got != body {
+		t.Fatalf("expected %q got %q", body, got)
+	}
+}
+
 // Don't send the fragment/hash/# part of a URL to the server.
 func TestFragmentInURIRequest(t *testing.T) {
 	var req Request