Added error message that is displayed when stack can not be retrieved because of…

Added error message that is displayed when stack can not be retrieved because of IndexError in inspect.stack()

debug_toolbar_mongo/operation_tracker.py

@@ -36,7 +36,13 @@ def _get_stacktrace():
         except IndexError:
             # this is a work around because python's inspect.stack() sometimes fail
             # when jinja templates are on the stack
-            return []
+            return [(
+                "",
+                0,
+                "Error retrieving stack",
+                "Could not retrieve stack. IndexError exception occured in inspect.stack(). "
+                "This error might occur when jinja2 templates is on the stack.",
+            )]
         
         return _tidy_stacktrace(reversed(stack))
     else: