How can I check if a file exists in gawk?

Hi

I'm writing an awk script that takes a path as a variable using -v. In
the BEGIN section I need to parse
this file using:

while(getline < path)
{
:
:
}

Problem is , if the file doesn't exist it just hangs. How can I check
if the file exists in the first place? I'd
rather avoid using system() if possible as the script needs to be OS
portable.

Thanks for any help

B2003