ignore broken unicode chars

lib.go

@@ -1,7 +1,10 @@
 // Package textedit provides a non-regexp, streaming editor to apply basic text manipulation.
 package textedit
 
-import "io"
+import (
+	"io"
+	"unicode"
+)
 
 // Editor instances can be used to edit a text stream. It is expected from the implementations to be reusable
 // with fresh state after the Flush was called on the enclosing writer.
@@ -109,6 +112,10 @@ func (w *Writer) write(r []rune) error {
 	}
 
 	for _, ri := range r {
+		if ri == unicode.ReplacementChar {
+			continue
+		}
+
 		rr, s := w.editor.Edit(ri, w.state)
 		if _, err := w.out.Write([]byte(string(rr))); err != nil {
 			w.err = err

lib_test.go

@@ -75,6 +75,22 @@ func TestWriteRune(t *testing.T) {
 	}
 }
 
+func TestBrokenUnicode(t *testing.T) {
+	var b bytes.Buffer
+	w := textedit.New(&b)
+	if _, err := w.Write([]byte("foo \xc2bar baz")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := w.Flush(); err != nil {
+		t.Fatal(err)
+	}
+
+	if b.String() != "foo bar baz" {
+		t.Fatal(b.String())
+	}
+}
+
 func TestFailingWriter(t *testing.T) {
 	t.Run("after write", func(t *testing.T) {
 		var b bytes.Buffer