doc: add missing variable "pointer" to make C compiler really happy (plugin API reference)

doc/en/weechat_plugin_api.en.adoc

@@ -192,6 +192,7 @@ command_double_cb (const void *pointer, void *data,
                    int argc, char **argv, char **argv_eol)
 {
     /* make C compiler happy */
+    (void) pointer;
     (void) data;
     (void) buffer;
     (void) argv;

doc/fr/weechat_plugin_api.fr.adoc

@@ -197,6 +197,7 @@ commande_double_cb (const void *pointer, void *data,
                     int argc, char **argv, char **argv_eol)
 {
     /* pour que le compilateur C soit content */
+    (void) pointer;
     (void) data;
     (void) buffer;
     (void) argv;

doc/it/weechat_plugin_api.it.adoc

@@ -210,6 +210,7 @@ command_double_cb (const void *pointer, void *data,
                    int argc, char **argv, char **argv_eol)
 {
     /* fa felice il compilatore C */
+    (void) pointer;
     (void) data;
     (void) buffer;
     (void) argv;

doc/ja/weechat_plugin_api.ja.adoc

@@ -198,6 +198,7 @@ command_double_cb (const void *pointer, void *data,
                    int argc, char **argv, char **argv_eol)
 {
     /* C 言語コンパイラ向けに必要 */
+    (void) pointer;
     (void) data;
     (void) buffer;
     (void) argv;