gthread: Fix "zero as null pointer" warning
When compiling a program using glib with -Wzero-as-null-pointer-constant warnings enabled, the compiler warns about this type check in the g_once_init_enter macro. Fix by replacing "0" with "NULL".
When compiling a program using glib with -Wzero-as-null-pointer-constant warnings enabled, the compiler warns about this type check in the g_once_init_enter macro. Fix by replacing "0" with "NULL".