add go mod stuff and fix log.Errorf

go.mod

@@ -0,0 +1,13 @@
+module github.com/brentp/vcfgo
+
+go 1.22.5
+
+require (
+	github.com/brentp/irelate v0.0.1
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
+)
+
+require (
+	github.com/kr/pretty v0.2.1 // indirect
+	github.com/kr/text v0.1.0 // indirect
+)

go.sum

@@ -0,0 +1,9 @@
+github.com/brentp/irelate v0.0.1 h1:uVK5yw9XaDzi+04zbob4q9K6u2e5dcdqH7UO1+6Keo0=
+github.com/brentp/irelate v0.0.1/go.mod h1:Ct+JzyZC+JSi9WUkw3IGWc/j0yYEt4235wKCfLOKN54=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=

header.go

@@ -226,7 +226,8 @@ func parseHeaderExtraKV(kv string) ([]string, error) {
 	kvpair := strings.SplitN(kv, "=", 2)
 
 	if len(kvpair) != 2 {
-		return nil, fmt.Errorf("header error in extra field: %s", kv)
+        kvpair = append(kvpair, "")
+		return kvpair, fmt.Errorf("header error in extra field: %s", kv)
 	}
 	return kvpair, nil
 }