nag_gpu was declared and initialized after the first two goto
shutdown jump points (config load failure, server start failure).
Reaching shutdown: via either path means nag_gpu.client is read
at "if (nag_gpu.client != NULL)" before its initializer ever ran
— an indeterminate value per C11, not guaranteed to be NULL.
This moves the declaration/initialization before
load_main_config, so nag_gpu is always initialized by the time
any goto shutdown path is reached.
Not independently reproduced as an observed crash; the fix
addresses undefined behavior per the C standard regardless of
whether it manifests as a crash on any given stack layout.