Fix build with gcc-16 (deadbeef DDB_API_LEVEL >= 11).

Two forward-compat diagnostics gcc-16 now treats as hard errors:
  * get_time() is declared void but ended with `return 0;`
    (-Wreturn-mismatch).
  * the action callbacks used the pre-API-11 `int ctx` signature;
    DB_plugin_action_callback2_t now takes ddb_action_context_t.

Upstream unmaintained since 2015; carried locally.
--- a/bookmark.c
+++ b/bookmark.c
@@ -66,7 +66,7 @@
     *hr = time/3600;
     *mn = (time-(*hr)*3600)/60;
     *sc = time-(*hr)*3600-(*mn)*60;
-    return 0;
+    return;
 }
 
 static int
@@ -218,7 +218,7 @@
 }
 
 static int
-bookmark_action_select (DB_plugin_action_t *action, int ctx)
+bookmark_action_select (DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     DB_playItem_t *it = bookmark_get_selected_track (ctx);
     if (!it) {
@@ -233,7 +233,7 @@
 }
 
 static int
-bookmark_action_reset (DB_plugin_action_t *action, int ctx)
+bookmark_action_reset (DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     DB_playItem_t *it = bookmark_get_selected_track (ctx);
     if (!it) {
@@ -249,7 +249,7 @@
 }
 
 static int
-bookmark_action_resume (DB_plugin_action_t *action, int ctx)
+bookmark_action_resume (DB_plugin_action_t *action, ddb_action_context_t ctx)
 {
     DB_playItem_t *it = bookmark_get_selected_track (ctx);
     if (!it) {