Use empty va_list in place of nullptr in openconnect external browser support
requested to merge binaryeater/plasma-nm:bugfix/openconnect_external_browser_va_args_handling into master
This change also refactors va_list declarations in openconnectauthworkerthread.cpp to avoid referring to them as pointers since pointer types may not be convertitble to a va_list depending on architecture ABI.
Fixes: 408cca64 ("Add support for openconnect_set_external_browser_callback introduced in openconnect v9.0 (libopenconnect 5.8) using QDesktopServices") Signed-off-by: Rahul Rameshbabu sergeantsagara@protonmail.com