RecordReader: fix regex reading even more

The re type was not in empty, meaning it was not tracked properly and
well, things fell apart from there.

pkg/kgo/record_formatter.go

@@ -1421,7 +1421,8 @@ func (r *readKind) empty() bool {
 		r.size == 0 &&
 		r.sizefn == nil &&
 		r.handoff == nil &&
-		r.delim == nil
+		r.delim == nil &&
+		r.re == nil
 }
 
 type readParse struct {
@@ -1461,6 +1462,7 @@ func (r *RecordReader) next(rec *Record) error {
 		default:
 			err = r.readDelim(fn.read.delim) // we *always* fall back to delim parsing
 		}
+
 		switch err {
 		default:
 			return err

pkg/kgo/record_formatter_test.go

@@ -433,6 +433,22 @@ func TestRecordReader(t *testing.T) {
 			},
 		},
 
+		{
+			layout: `%v{re#...?#}\n`,
+			in:     "abc\n",
+			exp: []*Record{
+				StringRecord("abc"),
+			},
+		},
+
+		{
+			layout: `%v{re#...?#}\n`,
+			in:     "ab\n",
+			exp: []*Record{
+				StringRecord("ab"),
+			},
+		},
+
 		{
 			layout: `%v{re#....#}`,
 			in:     "abc123",