Restore default behaviour for stamps

@mdosch discovered that we now don't print `:` for messages from others
anymore.

Until
https://github.com/profanity-im/profanity/pull/1663#issuecomment-1114625151
is fixed lets restore the default behaviour to always add `:` in
`_win_print_internal()`.

The result will be that a stamp set to `-->` will also look like `-->:`.

src/ui/window.c

@@ -1602,7 +1602,7 @@ _win_print_internal(ProfWin* window, const char* show_char, int pad_indent, GDat
             offset = 4;
             me_message = TRUE;
         } else {
-            wprintw(window->layout->win, "%s ", from);
+            wprintw(window->layout->win, "%s: ", from);
             wattroff(window->layout->win, colour);
         }
     }