introduce auto_gcharv

This also fixes memory leaks in `_omemo_autocomplete()`.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

src/common.c

@@ -78,6 +78,14 @@ auto_free_gchar(gchar** str)
     g_free(*str);
 }
 
+void
+auto_free_gcharv(gchar*** args)
+{
+    if (args == NULL)
+        return;
+    g_strfreev(*args);
+}
+
 void
 auto_free_char(char** str)
 {