Show an info message if some of the paths are skipped during a drag&drop.

Related to #10544

gajim/chat_control_base.py

@@ -967,12 +967,13 @@ class ChatControlBase(ChatCommandProcessor, CommandTools, EventHelper):
         self.xml.drop_area.set_no_show_all(False)
         self.xml.drop_area.show_all()
 
-    def drag_data_file_transfer(self, selection):
+    def drag_data_file_transfer(self, selection: Gtk.SelectionData) -> None:
         # we may have more than one file dropped
         uri_splitted = selection.get_uris()
         for uri in uri_splitted:
             path = helpers.get_file_path_from_dnd_dropped_uri(uri)
             if not os.path.isfile(path):  # is it a file?
+                self.add_info_message(_("The following file could not be accessed and was not uploaded: ") + path)
                 continue
 
             self._start_filetransfer(path)

gajim/common/helpers.py

@@ -352,7 +352,7 @@ def build_command(executable, parameter):
     command = '%s "%s"' % (executable, parameter)
     return command
 
-def get_file_path_from_dnd_dropped_uri(uri):
+def get_file_path_from_dnd_dropped_uri(uri: str) -> str:
     path = urllib.parse.unquote(uri) # escape special chars
     path = path.strip('\r\n\x00') # remove \r\n and NULL
     # get the path to file