boxes: Footer message if tab key pessed while editing a private message.

Author: Subhasish-Behera

zulipterminal/ui_tools/boxes.py

@@ -927,6 +927,10 @@ def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
                 else:
                     header.focus_col = self.FOCUS_HEADER_BOX_STREAM
             else:
+                if self.msg_edit_state:
+                    self.model.controller.report_error(
+                        [" Recipient(s) can not be edited while editing a PM."]
+                    )
                 header.focus_col = self.FOCUS_HEADER_BOX_RECIPIENT
 
         key = super().keypress(size, key)