obs-scripting: Make callback "removed" variable atomic

Makes the callback variable "removed" atomic, and on script unload,
first sets all callbacks to removed before actually unloading the script
out of a safety precaution. (See note at the bottom for further details)

This minimizes the possibility of a race condition where the script
callback could be called while those callbacks were being removed.

Big note for this change, this change should eventually be replaced with
a reference counting ownership method where script callbacks can hold a
reference and share ownership of the script if it's still alive while
the script callback is being called. That way the script callbacks can
safely execute. May require a fair amount of reworking of the script
object.

deps/obs-scripting/obs-scripting-python.h

@@ -195,6 +195,7 @@ static inline bool py_error_(const char *func, int line)
 #define py_error() py_error_(__FUNCTION__, __LINE__)
 
 #define lock_python() PyGILState_STATE gstate = PyGILState_Ensure()
+#define relock_python() gstate = PyGILState_Ensure()
 #define unlock_python() PyGILState_Release(gstate)
 
 struct py_source;