Cleanup: py-gpu error checks

Move gpu initialization checks to the start of each function instead
of mixing with argument parsing.

source/blender/python/gpu/gpu_py_api.h

@@ -25,10 +25,13 @@
 #ifndef __GPU_PY_API_H__
 #define __GPU_PY_API_H__
 
-bool bpygpu_is_initialized(void);
 
 int bpygpu_ParsePrimType(PyObject *o, void *p);
 
 PyObject *BPyInit_gpu(void);
 
+bool bpygpu_is_initialized_or_error(void);
+#define BPYGPU_IS_INIT_OR_ERROR_OBJ if (UNLIKELY(!bpygpu_is_initialized_or_error())) { return NULL; } ((void)0)
+#define BPYGPU_IS_INIT_OR_ERROR_INT if (UNLIKELY(!bpygpu_is_initialized_or_error())) { return -1; } ((void)0)
+
 #endif  /* __GPU_PY_API_H__ */