fix initialize Compiler when user_defined_options is None

Author: seiko2plus

mesonbuild/interpreter/interpreter.py

@@ -1135,7 +1135,7 @@ def set_backend(self) -> None:
             return
         from ..backend import backends
 
-        if OptionKey('genvslite') in self.user_defined_options.cmd_line_options:
+        if self.user_defined_options and OptionKey('genvslite') in self.user_defined_options.cmd_line_options:
             # Use of the '--genvslite vsxxxx' option ultimately overrides any '--backend xxx'
             # option the user may specify.
             backend_name = self.coredata.optstore.get_value_for(OptionKey('genvslite'))