If rtlsdr_read_async returns early, the device is probably hosed, give up;

rely on the caller of dump1090 to restart.

sdr_rtlsdr.c

@@ -362,10 +362,11 @@ void rtlsdrRun()
 
     start_cpu_timing(&rtlsdr_thread_cpu);
 
-    while (!Modes.exit) {
     rtlsdr_read_async(RTLSDR.dev, rtlsdrCallback, NULL,
                       /* MODES_RTL_BUFFERS */ 4,
                       MODES_RTL_BUF_SIZE);
+    if (!Modes.exit) {
+        log_with_timestamp("rtlsdr_read_async returned unexpectedly, probably lost the USB device, bailing out");
     }
 }