fix coverity resource leak in windows_plugin_add

13056 Resource leak
In windows_plugin_add(): Leak of memory or pointers to system resources (CWE-404)
(cherry picked from commit ba92e5287970d09c4c280eda56c4e58bc064a2c1)

ldap/servers/plugins/replication/windows_private.c

@@ -1246,6 +1246,8 @@ windows_plugin_add(void **theapi, int maxapi)
             PR_INSERT_BEFORE(wpi, elem);
             wpi = NULL; /* owned by list now */
         }
+        /* if we got here and wpi is not NULL we need to free wpi */
+        slapi_ch_free((void **)&wpi);
         return 0;
     }
     return -1;