change toPlainText to exclude image

lib/src/models/documents/nodes/line.dart

@@ -402,7 +402,7 @@ class Line extends Container<Leaf?> {
       }
     }
 
-    // Need to add current line's style or parent block's style?
+    // TODO: add line style and parent's block style
 
     final remaining = len - local;
     if (remaining > 0) {
@@ -452,6 +452,9 @@ class Line extends Container<Leaf?> {
     final res = _getPlainText(offset, len);
     if (res.length == 1) {
       final data = queryChild(offset, true);
+      if ((data.node as Leaf) is Embed) {
+        return '';
+      }
       final text = res.single.item2;
       return text.substring(data.offset, data.offset + len);
     }
@@ -460,16 +463,22 @@ class Line extends Container<Leaf?> {
     // Adjust first node
     final firstNodeLen = res[1].item1;
     var text = res[0].item2;
-    total.add(text.substring(text.length - firstNodeLen));
+    if (text != Embed.kObjectReplacementCharacter) {
+      total.add(text.substring(text.length - firstNodeLen));
+    }
 
     for (var i = 1; i < res.length - 1; i++) {
-      total.add(res[i].item2);
+      if (text != Embed.kObjectReplacementCharacter) {
+        total.add(res[i].item2);
+      }
     }
 
     // Adjust last node
     final lastNodeLen = len - res[res.length - 1].item1;
     text = res[res.length - 1].item2;
-    total.add(text.substring(0, lastNodeLen));
+    if (text != Embed.kObjectReplacementCharacter) {
+      total.add(text.substring(0, lastNodeLen));
+    }
     return total.join();
   }