Crash after dragging multiple items from clipboard to gallery

I copied 7 items from the Media List to the clipboard. I then opened a
Person, and dragged one Media Item to the Gallery. I then clicked and
dragged to highlight the remaining 6 items at once. On dragging them to
the gallery, it crashed.

2989475: ERROR: grampsapp.py: line 145: Unhandled exception
Traceback (most recent call last):
File "C:\Program
Files\GrampsAIO64-4.2.5\gramps\gui\editors\displaytabs\gallerytab.py",
line 475, in drag_data_received
(mytype, selfid, obj, row_from) = pickle.loads(sel_data.get_data())
ValueError: too many values to unpack (expected 4)

Fixes #9984.

gramps/gui/editors/displaytabs/gallerytab.py

@@ -467,8 +467,21 @@ class GalleryTab(ButtonTab, DbGUIElement):
         and decide if this is a move or a reorder.
         """
         if sel_data and sel_data.get_data():
+            sel_list = []
             try:
-                (mytype, selfid, obj, row_from) = pickle.loads(sel_data.get_data())
+                rets = pickle.loads(sel_data.get_data())
+
+                # single dnd item
+                if isinstance(rets, tuple):
+                    sel_list.append(rets)
+
+                # multiple dnd items
+                elif isinstance(rets, list):
+                    for ret in rets:
+                        sel_list.append(pickle.loads(ret))
+
+                for sel in sel_list:
+                    (mytype, selfid, obj, row_from) = sel
 
                     # make sure this is the correct DND type for this object
                     if mytype == self._DND_TYPE.drag_type: