Fix memory leak in Context.temp_override

Add missing check as the context override dict may have been copied
since it was assigned, also initialize the context manager with
PyType_Ready, while it didn't cause any errors - it's expected
that all types are initialized.

source/blender/python/intern/bpy_rna_context.h

@@ -12,6 +12,8 @@ extern "C" {
 
 extern PyMethodDef BPY_rna_context_temp_override_method_def;
 
+void bpy_rna_context_types_init(void);
+
 #ifdef __cplusplus
 }
 #endif