Allow disabling keepalive inference for constructors

Author: auscompgeek

robotpy_build/autowrap/cxxparser.py

@@ -1105,7 +1105,7 @@ def _on_class_method(
 
         # automatically retain references passed to constructors if the
         # user didn't specify their own keepalive
-        if is_constructor and not method_data.keepalive:
+        if is_constructor and method_data.keepalive is None:
             for i, pctx in enumerate(fctx.filtered_params):
                 if pctx.full_cpp_type.endswith("&"):
                     fctx.keepalives.append((1, i + 2))