irc: check if arguments are not NULL in some infos

Affected infos:

- irc_server_isupport
- irc_server_isupport_value
- irc_server_cap
- irc_server_cap_value

ChangeLog.adoc

@@ -58,6 +58,7 @@ Bug fixes::
   * core: fix crash when a custom bar item name is already used by a default bar item (issue #2034)
   * core: fix random timeouts when a lot of concurrent processes are launched with hook_process (issue #2033)
   * api: return NULL instead of empty infolist "key" when context is not found
+  * irc: check if arguments are not NULL in some infos
   * irc: fix info "irc_is_message_ignored" (issue #2059)
   * irc: fix display of self messages when the message split fails due to inconsistent max lengths sent by the server in message 005
   * irc: display messages 730/731 (monitored nicks online/offline) even if command `/notify` was not used (issue #2049)

src/plugins/irc/irc-info.c

@@ -344,6 +344,9 @@ irc_info_info_irc_server_isupport_cb (const void *pointer, void *data,
     (void) data;
     (void) info_name;
 
+    if (!arguments || !arguments[0])
+        return NULL;
+
     isupport_value = NULL;
     pos_comma = strchr (arguments, ',');
     if (pos_comma)
@@ -382,6 +385,9 @@ irc_info_info_irc_server_isupport_value_cb (const void *pointer, void *data,
     (void) data;
     (void) info_name;
 
+    if (!arguments || !arguments[0])
+        return NULL;
+
     isupport_value = NULL;
     pos_comma = strchr (arguments, ',');
     if (pos_comma)
@@ -420,6 +426,9 @@ irc_info_info_irc_server_cap_cb (const void *pointer, void *data,
     (void) data;
     (void) info_name;
 
+    if (!arguments || !arguments[0])
+        return NULL;
+
     has_cap = 0;
     pos_comma = strchr (arguments, ',');
     if (pos_comma)
@@ -458,6 +467,9 @@ irc_info_info_irc_server_cap_value_cb (const void *pointer, void *data,
     (void) data;
     (void) info_name;
 
+    if (!arguments || !arguments[0])
+        return NULL;
+
     cap_value = NULL;
     pos_comma = strchr (arguments, ',');
     if (pos_comma)