fixes crash when trying to copy image

src/transcript/layouts/bubble-layout.vala

@@ -63,6 +63,8 @@ private abstract class BubbleLayout : Object, ChatItemLayout
 
     public abstract void draw_content(Snapshot snapshot);
 
+    public abstract void copy(Gdk.Clipboard clipboard);
+
     private void draw_background(Snapshot snapshot) 
     {
         var width = get_width();

src/transcript/layouts/chat-item-layout.vala

@@ -10,4 +10,5 @@ interface ChatItemLayout : Object
     public abstract float get_width();
 
     public abstract void draw(Snapshot snapshot);
+    public abstract void copy(Gdk.Clipboard clipboard);
 }

src/transcript/layouts/date-item-layout.vala

@@ -47,4 +47,8 @@ class DateItemLayout : Object, ChatItemLayout {
         
         snapshot.restore();
     }
+
+    public void copy(Gdk.Clipboard clipboard) {
+        clipboard.set_text(layout.get_text());
+    }
 }

src/transcript/layouts/image-bubble-layout.vala

@@ -132,4 +132,8 @@ private class ImageBubbleLayout : BubbleLayout
 
         snapshot.restore();
     }
+
+    public override void copy(Gdk.Clipboard clipboard) {
+        clipboard.set_texture(cached_texture);
+    }
 } 

src/transcript/layouts/sender-annotation-layout.vala

@@ -54,4 +54,8 @@ private class SenderAnnotationLayout : Object, ChatItemLayout
 
         snapshot.restore();
     }
+
+    public void copy(Gdk.Clipboard clipboard) {
+        clipboard.set_text(sender);
+    }
 }

src/transcript/layouts/text-bubble-layout.vala

@@ -91,6 +91,10 @@ private class TextBubbleLayout : BubbleLayout
 
         snapshot.restore();
     }
+
+    public override void copy(Gdk.Clipboard clipboard) {
+        clipboard.set_text(message.text);
+    }
 }
 
 

src/transcript/transcript-drawing-area.vala

@@ -195,11 +195,7 @@ private class TranscriptDrawingArea : Widget
             y_offset += chat_item.get_height() + chat_item.vertical_padding;
             
             if (y_offset > bounding_box.y) {
-                var text_bubble = chat_item as TextBubbleLayout;
-                var text = text_bubble.message.text;
-
-                var clipboard = get_clipboard();
-                clipboard.set_text(text);
+                chat_item.copy(get_clipboard());
                 break;
             }
         }