doc: add arvg[2] in example of function string_split_command (plugin API reference)

doc/en/weechat_plugin_api.en.asciidoc

@@ -1626,6 +1626,7 @@ C example:
 char **argv = weechat_string_split_command ("/command1 arg;/command2", ';');
 /* result: argv[0] == "/command1 arg"
            argv[1] == "/command2"
+           argv[2] == NULL
 */
 weechat_free_split_command (argv);
 ----

doc/fr/weechat_plugin_api.fr.asciidoc

@@ -1658,6 +1658,7 @@ Exemple en C :
 char **argv = weechat_string_split_command ("/commande1 arg;/commande2", ';');
 /* résultat : argv[0] == "/commande1 arg"
               argv[1] == "/commande2"
+              argv[2] == NULL
 */
 weechat_free_split_command (argv);
 ----

doc/it/weechat_plugin_api.it.asciidoc

@@ -1692,6 +1692,7 @@ Esempio in C:
 char **argv = weechat_string_split_command ("/command1 arg;/command2", ';');
 /* result: argv[0] == "/command1 arg"
            argv[1] == "/command2"
+           argv[2] == NULL
 */
 weechat_free_split_command (argv);
 ----

doc/ja/weechat_plugin_api.ja.asciidoc

@@ -1628,6 +1628,7 @@ C 言語での使用例:
 char **argv = weechat_string_split_command ("/command1 arg;/command2", ';');
 /* result: argv[0] == "/command1 arg"
            argv[1] == "/command2"
+           argv[2] == NULL
 */
 weechat_free_split_command (argv);
 ----