Update text_line for handling Embed

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

@@ -26,11 +26,7 @@ class Line extends Container<Leaf?> {
 
   /// Returns `true` if this line contains an embedded object.
   bool get hasEmbed {
-    if (childCount != 1) {
-      return false;
-    }
-
-    return children.single is Embed;
+    return children.any((child) => child is Embed);
   }
 
   /// Returns next [Line] or `null` if this is the last line in the document.

lib/src/widgets/text_line.dart

@@ -39,12 +39,17 @@ class TextLine extends StatelessWidget {
   Widget build(BuildContext context) {
     assert(debugCheckHasMediaQuery(context));
 
-    // In rare circumstances, the line could contain an Embed & a Text of
-    // newline, which is unexpected and probably we should find out the
-    // root cause
-    final childCount = line.childCount;
-    if (line.hasEmbed || (childCount > 1 && line.children.first is Embed)) {
-      final embed = line.children.first as Embed;
+    if (line.hasEmbed) {
+      if (line.childCount == 1) {
+        // For video, it is always single child
+        final embed = line.children.single as Embed;
+        return EmbedProxy(embedBuilder(context, embed, readOnly));
+      }
+
+      // The line could contain more than one Embed & more than one Text
+      // TODO: handle more than one Embed
+      final embed =
+          line.children.firstWhere((child) => child is Embed) as Embed;
       return EmbedProxy(embedBuilder(context, embed, readOnly));
     }