core, plugins: return "0x0" instead of "(nil)" for pointers formatted in strings

This is a partial revert of the commit
965beb37de.

src/plugins/irc/irc-bar-item.c

@@ -658,7 +658,8 @@ irc_bar_item_focus_buffer_nicklist (const void *pointer, void *data,
             ptr_nick = irc_nick_search (ptr_server, ptr_channel, nick);
             if (ptr_nick)
             {
-                snprintf (str_value, sizeof (str_value), "%p", ptr_nick);
+                snprintf (str_value, sizeof (str_value),
+                          "0x%lx", (unsigned long)ptr_nick);
                 weechat_hashtable_set (info, "irc_nick", str_value);
 
                 if (ptr_nick->host)

src/plugins/irc/irc-info.c

@@ -57,7 +57,7 @@ irc_info_create_string_with_pointer (char **string, void *pointer)
         *string = malloc (64);
         if (*string)
         {
-            snprintf (*string, 64, "%p", pointer);
+            snprintf (*string, 64, "0x%lx", (unsigned long)pointer);
         }
     }
 }

src/plugins/irc/irc-typing.c

@@ -143,8 +143,8 @@ irc_typing_channel_set_nick (struct t_irc_channel *channel, const char *nick,
     char signal_data[1024];
 
     snprintf (signal_data, sizeof (signal_data),
-              "%p;%s;%s",
-              channel->buffer,
+              "0x%lx;%s;%s",
+              (unsigned long)channel->buffer,
               (state == IRC_CHANNEL_TYPING_STATE_ACTIVE) ? "typing" :
               ((state == IRC_CHANNEL_TYPING_STATE_PAUSED) ? "paused" : "off"),
               nick);