Vulpix, you can remane that key as unsane said.
unsane, I wonder why that key is needed at all? Can't you just loop through all settings until you find one that doesn't exist?
Smth like that:
			for (lvi.iItem = 0; ; lvi.iItem++)
			{ 
				mir_snprintf(setting, SIZEOF(setting), TOX_SETTINGS_NODE_IPV4, lvi.iItem);
                                char *szIPv4 = db_get_sa(NULL, MODULE, setting);
                                if (szIPv4 == NULL) break; // break if setting doesn't exist
				mir_snprintf(setting, SIZEOF(setting), TOX_SETTINGS_NODE_IPV6, lvi.iItem);
                                char *szIPv6 = db_get_sa(NULL, MODULE, setting);
                                if (szIPv6 == NULL) {
                                       mir_free(szIPv4);
                                       break; // break if setting doesn't exist
                                 }
				mir_snprintf(setting, SIZEOF(setting), TOX_SETTINGS_NODE_PKEY, lvi.iItem);
                                char *szKey = db_get_sa(NULL, MODULE, setting);
                                if (szKey == NULL) {
                                       mir_free(szIPv4);
                                       mir_free(szIPv6);
                                       break; // break if setting doesn't exist
                                 }
				lvi.iImage = -1;
				lvi.mask = LVIF_TEXT | LVIF_IMAGE;
				lvi.iSubItem = 0;
				lvi.pszText = szIPv4;
				SendMessage(hwndList, LVM_INSERTITEMA, 0, (LPARAM)&lvi);
				lvi.iSubItem = 1;
				lvi.pszText = szIPv6;
				SendMessage(hwndList, LVM_SETITEMA, 0, (LPARAM)&lvi);
				mir_snprintf(setting, SIZEOF(setting), TOX_SETTINGS_NODE_PORT, lvi.iItem);
				int port = db_get_w(NULL, MODULE, setting, 0);
				if (port > 0)
				{
					char portNum[10];
					itoa(port, portNum, 10);
					lvi.pszText = mir_strdup(portNum);
				}
				lvi.iSubItem = 2;
				SendMessage(hwndList, LVM_SETITEMA, 0, (LPARAM)&lvi);
				lvi.iSubItem = 3;
				lvi.pszText = szKey;
				SendMessage(hwndList, LVM_SETITEMA, 0, (LPARAM)&lvi);
				lvi.mask = LVIF_IMAGE;
				lvi.iSubItem = 4;
				lvi.iImage = 0;
				ListView_SetItem(hwndList, &lvi);
				lvi.iSubItem = 5;
				lvi.iImage = 1;
				ListView_SetItem(hwndList, &lvi);
			}