[geary] Don't crash when attempting to display a 0-sized inline image.

[Michael Gratton <mjog src gnome org>]

commit 7ba13e934d13eac984f34541ebd040d40bf550df
Author: Michael James Gratton <mike vee net>
Date:   Fri Nov 18 11:44:23 2016 +1100

    Don't crash when attempting to display a 0-sized inline image.
    
    * src/client/conversation-viewer/conversation-message.vala
      (ConversationMessage::clean_html_markup): Check the image buffer
      actually has some bytes before processing it.

 .../conversation-viewer/conversation-message.vala  |   50 ++++++++++---------
 1 files changed, 26 insertions(+), 24 deletions(-)
---
diff --git a/src/client/conversation-viewer/conversation-message.vala 
b/src/client/conversation-viewer/conversation-message.vala
index 229c52d..bd3f545 100644
--- a/src/client/conversation-viewer/conversation-message.vala
+++ b/src/client/conversation-viewer/conversation-message.vala
@@ -1023,30 +1023,32 @@ public class ConversationMessage : Gtk.Grid {
                 if (!replaced_content_ids.contains(content_id)) {
                     string? filename = message.get_content_filename_by_mime_id(content_id);
                     Geary.Memory.Buffer image_content = message.get_content_by_mime_id(content_id);
-                    Geary.Memory.UnownedBytesBuffer? unowned_buffer =
-                        image_content as Geary.Memory.UnownedBytesBuffer;
-                    
-                    // Get the content type.
-                    string guess;
-                    if (unowned_buffer != null)
-                        guess = ContentType.guess(null, unowned_buffer.to_unowned_uint8_array(), null);
-                    else
-                        guess = ContentType.guess(null, image_content.get_uint8_array(), null);
-                    
-                    string mimetype = ContentType.get_mime_type(guess);
-                    
-                    // Replace the SRC to a data URI, the class to a known label for the popup menu,
-                    // and the ALT to its filename, if supplied
-                    img.remove_attribute("src");  // Work around a WebKitGTK+ crash. Bug 764152
-                    img.set_attribute("src", Util.DOM.assemble_data_uri(mimetype, image_content));
-                    img.class_list.add(DATA_IMAGE_CLASS);
-                    if (!Geary.String.is_empty(filename))
-                        img.set_attribute("alt", filename);
-                    
-                    // stash here so inlined image isn't listed as attachment (esp. if it has no
-                    // Content-Disposition)
-                    inlined_content_ids.add(content_id);
-                    attachment_displayed_inline(content_id);
+                    if (image_content.size > 0) {
+                        Geary.Memory.UnownedBytesBuffer? unowned_buffer =
+                            image_content as Geary.Memory.UnownedBytesBuffer;
+
+                        // Get the content type.
+                        string guess;
+                        if (unowned_buffer != null)
+                            guess = ContentType.guess(null, unowned_buffer.to_unowned_uint8_array(), null);
+                        else
+                            guess = ContentType.guess(null, image_content.get_uint8_array(), null);
+
+                        string mimetype = ContentType.get_mime_type(guess);
+
+                        // Replace the SRC to a data URI, the class to a known label for the popup menu,
+                        // and the ALT to its filename, if supplied
+                        img.remove_attribute("src");  // Work around a WebKitGTK+ crash. Bug 764152
+                        img.set_attribute("src", Util.DOM.assemble_data_uri(mimetype, image_content));
+                        img.class_list.add(DATA_IMAGE_CLASS);
+                        if (!Geary.String.is_empty(filename))
+                            img.set_attribute("alt", filename);
+
+                        // stash here so inlined image isn't listed as attachment (esp. if it has no
+                        // Content-Disposition)
+                        inlined_content_ids.add(content_id);
+                        attachment_displayed_inline(content_id);
+                    }
                 } else {
                     // replaced by data: URI, remove this tag and let the inserted one shine through
                     img.parent_element.remove_child(img);