Prevent save thread from hanging on a quit

Without the condition to check if the thread should be running (e.g., the call
to run_threads()) the save thread hangs waiting for blocks to be filled and does
not register the signal interrupt correctly.

versions/scalloping/src/flag_beamsave_thread.c

@@ -49,7 +49,7 @@ static void * run(hashpipe_thread_args_t * args) {
     while (run_threads()) {
         
         // Wait for input buffer block to be filled
-        while ((rv=flag_gpu_beamformer_output_databuf_wait_filled(db_in, curblock_in)) != HASHPIPE_OK) {
+        while ((rv=flag_gpu_beamformer_output_databuf_wait_filled(db_in, curblock_in)) != HASHPIPE_OK && run_threads()) {
             if (rv==HASHPIPE_TIMEOUT) {
                 hashpipe_status_lock_safe(&st);
                 hputs(st.buf, status_key, "waiting for free block");