m_option: add -clr to keyvalue list options

Seems to have been omitted by mistake and nobody ever noticed.

DOCS/interface-changes/list-option.txt

@@ -1,2 +1,3 @@
 undeprecate list option suffixes that work with multiple items
 add `-del` to string list and keyvalue list options
+add `-clr` to keyvalue list options

DOCS/man/mpv.rst

@@ -676,6 +676,7 @@ Suffix        Meaning
 -set          Set a list of items (using ``,`` as separator)
 -append       Append a single item (escapes for the key, no escapes for the value)
 -add          Append 1 or more items (same syntax as -set)
+-clr          Clear the option (remove all items)
 -del          Delete 1 or more keys if present (same syntax as -set)
 -remove       Delete item by key if present (does not interpret escapes)
 ============= ===============================================

options/m_option.c

@@ -1718,6 +1718,10 @@ static int parse_keyvalue_list(struct mp_log *log, const m_option_t *opt,
         append = true;
     } else if (bstr_endswith0(name, "-append")) {
         append = full_value = true;
+    } else if (bstr_endswith0(name, "-clr")) {
+        if (dst)
+            free_str_list(dst);
+        return 0;
     } else if (op == OP_DEL || op == OP_REMOVE) {
         int n = 0;
         char **res = separate_input_param(opt, param, &n, op);
@@ -1861,6 +1865,7 @@ const m_option_type_t m_option_type_keyvalue_list = {
     .actions = (const struct m_option_action[]){
         {"add"},
         {"append"},
+        {"clr",         M_OPT_TYPE_OPTIONAL_PARAM},
         {"del"},
         {"set"},
         {"remove"},