Fix #104061: Python GPU module unusable after too early import

Add-ons may attempt to load the GPU module in background mode when no GPU
context has been initialized yet. This would give an error on import.

If then later the GPU context does get initialized, for example for a
render engine, import would still fail as the module is cached.

This reverts commit d7f124f06f, and again
throws errors in methods and constructors instead of module import.

Pull Request: https://projects.blender.org/blender/blender/pulls/123395

source/blender/python/gpu/gpu_py_shader.cc

@@ -99,6 +99,8 @@ static int pygpu_shader_uniform_location_get(GPUShader *shader,
 
 static PyObject *pygpu_shader__tp_new(PyTypeObject * /*type*/, PyObject *args, PyObject *kwds)
 {
+  BPYGPU_IS_INIT_OR_ERROR_OBJ;
+
   struct {
     const char *vertexcode;
     const char *fragcode;
@@ -948,6 +950,8 @@ PyDoc_STRVAR(
     "   :rtype: :class:`bpy.types.GPUShader`\n");
 static PyObject *pygpu_shader_from_builtin(PyObject * /*self*/, PyObject *args, PyObject *kwds)
 {
+  BPYGPU_IS_INIT_OR_ERROR_OBJ;
+
   PyC_StringEnum pygpu_bultinshader = {pygpu_shader_builtin_items};
   PyC_StringEnum pygpu_config = {pygpu_shader_config_items, GPU_SHADER_CFG_DEFAULT};
 
@@ -992,6 +996,8 @@ PyDoc_STRVAR(
     "   :rtype: :class:`bpy.types.GPUShader`\n");
 static PyObject *pygpu_shader_create_from_info(BPyGPUShader * /*self*/, BPyGPUShaderCreateInfo *o)
 {
+  BPYGPU_IS_INIT_OR_ERROR_OBJ;
+
   if (!BPyGPUShaderCreateInfo_Check(o)) {
     PyErr_Format(PyExc_TypeError, "Expected a GPUShaderCreateInfo, got %s", Py_TYPE(o)->tp_name);
     return nullptr;
@@ -1080,7 +1086,7 @@ PyObject *bpygpu_shader_init()
 {
   PyObject *submodule;
 
-  submodule = bpygpu_create_module(&pygpu_shader_module_def);
+  submodule = PyModule_Create(&pygpu_shader_module_def);
 
   return submodule;
 }