Thankfully this doesn't happen!!!

(I was ready to complain about rotten implementations...=)

Probably saved by one of these special magic behaviors of while

UPDATE:here it is

from perlop#I/O-Operators

The following lines are equivalent:

           while (defined($_ = <STDIN>)) { print; }
           while ($_ = <STDIN>) { print; }
           while (<STDIN>) { print; }
           for (;<STDIN>;) { print; }
           print while defined($_ = <STDIN>);
           print while ($_ = <STDIN>);
           print while <STDIN>;
[download]

This also behaves similarly, but avoids $_ :

           while (my $line = <STDIN>) { print $line }
[download]

In these loop constructs, the assigned value (whether assignment is automatic or explicit) is then tested to see whether it is defined. The defined test avoids problems where line has a string value that would be treated as false by Perl, for example a "" or a "0" with no trailing newline. If you really mean for such values to terminate the loop, they should be tested for explicitly:

doesn't mention readdir but I think it's a similar case (and a documentation hole)