devhsmsrc: Change if->while and continuously try to fill filenamequeue until filename added

Bug fix for devshmsrc that is causing Sig11 errors in gstlal_inspiral jobs.

In the case of timeout or time reversal, no filename is added to to the queue. Then, the script attempts to pop something off the queue thereby causing the segfault. By changing the if to a while, in the case there is a time reversal and nothing is added to the queue, then it will continue to try to add filenames to the queue.