Fix crash when calling pybind11::print in a subsystem:windows build

in line: file = module_::import("sys").attr("stdout");   the file will be none in a windows application build. won't be catched since there's no exception, and crashed in later access

Author: oxine

include/pybind11/pybind11.h

@@ -3548,6 +3548,9 @@ PYBIND11_NOINLINE void print(const tuple &args, const dict &kwargs) {
         }
     }
 
+    if (file.is_none())
+        return;
+
     auto write = file.attr("write");
     write(std::move(line));
     write(kwargs.contains("end") ? kwargs["end"] : str("\n"));