command: make vf-metadata/af-metadata not query metadata twice

For simplicity, these properties usually query the metadata from the
filter twice, even if it's not technically needed at all. The reason for
this is mostly the horrible (and legacy) sub-path access (which is why
tag_property() is so complex).

But for simple cases, we can easily avoid double querying, so do that.
The benefit is performance (well, won't matter), and supporting filters
that reset information on query (for later).

player/command.c

@@ -1241,9 +1241,12 @@ static int get_tag_entry(int item, int action, void *arg, void *ctx)
     return m_property_read_sub(props, action, arg);
 }
 
+// tags can be NULL for M_PROPERTY_GET_TYPE. (In all other cases, tags must be
+// provided, even for M_PROPERTY_KEY_ACTION GET_TYPE sub-actions.)
 static int tag_property(int action, void *arg, struct mp_tags *tags)
 {
     switch (action) {
+    case M_PROPERTY_GET_NODE: // same as GET, because type==mpv_node
     case M_PROPERTY_GET: {
         mpv_node_list *list = talloc_zero(NULL, mpv_node_list);
         mpv_node node = {
@@ -1363,14 +1366,17 @@ static int mp_property_filter_metadata(void *ctx, struct m_property *prop,
         if (!chain)
             return M_PROPERTY_UNAVAILABLE;
 
-        struct mp_filter_command cmd = {
-            .type = MP_FILTER_COMMAND_GET_META,
-            .res = &metadata,
-        };
-        mp_output_chain_command(chain, mp_tprintf(80, "%.*s", BSTR_P(key)), &cmd);
+        if (ka->action != M_PROPERTY_GET_TYPE) {
+            struct mp_filter_command cmd = {
+                .type = MP_FILTER_COMMAND_GET_META,
+                .res = &metadata,
+            };
+            mp_output_chain_command(chain, mp_tprintf(80, "%.*s", BSTR_P(key)),
+                                    &cmd);
 
-        if (!metadata)
-            return M_PROPERTY_ERROR;
+            if (!metadata)
+                return M_PROPERTY_ERROR;
+        }
 
         int res;
         if (strlen(rem)) {