Fix bad request trailer panic

header.go

@@ -2736,7 +2736,11 @@ func (h *RequestHeader) parseHeaders(buf []byte) (int, error) {
 					continue
 				}
 				if caseInsensitiveCompare(s.key, strTrailer) {
-					err = h.SetTrailerBytes(s.value)
+					if nerr := h.SetTrailerBytes(s.value); nerr != nil {
+						if err == nil {
+							err = nerr
+						}
+					}
 					continue
 				}
 			}

http_test.go

@@ -3,6 +3,7 @@ package fasthttp
 import (
 	"bufio"
 	"bytes"
+	"encoding/base64"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -24,6 +25,11 @@ func TestInvalidTrailers(t *testing.T) {
 	if err == io.EOF {
 		t.Fatal(err)
 	}
+
+	b, _ := base64.StdEncoding.DecodeString("tCAKIDoKCToKICAKCToKICAKCToKIAogOgoJOgogIAoJOgovIC8vOi4KOh0KVFJhSUxlUjo9HT09HQpUUmFJTGVSOicQAApUUmFJTGVSOj0gHSAKCT09HQoKOgoKCgo=")
+	if err := (&Request{}).Read(bufio.NewReader(bytes.NewReader(b))); !strings.Contains(err.Error(), "error when reading request headers: invalid header key") {
+		t.Fatalf("%#v", err)
+	}
 }
 
 func TestResponseEmptyTransferEncoding(t *testing.T) {