osdep/w32_register: register url protocols if they don't exist yet

Some protocols may not exist, add them so the mapping to url handler
works correctly. Note that protocols are not removed, only the handler
is. They will remain unassociated, after unregister.

Fixes: #16832

osdep/w32_register.c

@@ -305,6 +305,22 @@ static void w32_register(struct MPContext *mpctx)
     mp_assert(safe_protocols);
     char *protocols_str = NULL;
     for (int i = 0; safe_protocols[i]; ++i) {
+        mp_require(strlen(safe_protocols[i]) < 41);
+        char *protocol_key = mp_tprintf(61, "Software\\Classes\\%s", safe_protocols[i]);
+        wchar_t *protocol_key_w = mp_from_utf8(tmp, protocol_key);
+
+        HKEY key;
+        LRESULT res = RegOpenKeyExW(root, protocol_key_w, 0, KEY_READ, &key);
+        if (res == ERROR_FILE_NOT_FOUND) {
+            // Add protocol definition only if it doesn't already exist
+            char *protocol_name = mp_tprintf(61, "URL:%s", safe_protocols[i]);
+            reg_add_str(log, root, protocol_key_w, NULL, mp_from_utf8(tmp, protocol_name));
+            reg_add_str(log, root, protocol_key_w, L"URL Protocol", L"");
+            reg_add_dwr(log, root, protocol_key_w, L"EditFlags", FTA_Show);
+        } else if (res == ERROR_SUCCESS) {
+            RegCloseKey(key);
+        }
+
         reg_add_str(log, root, KEY_MPV_CAPABILITIES L"\\URLAssociations",
                     mp_from_utf8(tmp, safe_protocols[i]),
                     MPV_PROG_ID("url"));