FIFO WAN issue if file of frame does exist

[ArcticSnow]

Here the mote tried sending a frame referenced in the FIFO list but the corresponding file does not exist (though the folder was existing). No idea why the file does not exist in the first place. Maybe we rebooted the mote at the time it was suppose to create the file, not sure...

1603877761.239 INFO Frame saved to FIFO bytes=33
1603877761.295 DEBUG 4G Switch on
1603877772.628 DEBUG 4G Enter PIN
1603877772.891 DEBUG 4G Check data connection
1603877783.234 DEBUG 4G Data connection OK
1603877783.290 DEBUG Sending frames...
1603877783.418 ERROR readFrame fail to open /data/049/544851.TXT
1603877783.582 DEBUG 4G time: 20/10/28,10:36:23+04"
1603877783.002 DEBUG 4G Switching off
1603877783.157 INFO Loop done in 23889 ms

The ls command shows the following file existing on the SD card:

> ls
DATA/          2020-10-22 11:33:30
  201022.TXT     2020-10-22 23:44:00 4709
  002/           2020-10-22 12:48:04
    201022.TXT     2020-10-22 23:53:08 49230
    201023.TXT     2020-10-23 13:53:08 51723
    201027.TXT     2020-10-27 22:48:10 5188
    201028.TXT     2020-10-28 08:48:08 6324
  201023.TXT     2020-10-23 14:56:00 1881
  201027.TXT     2020-10-27 23:56:00 4338
  003/           2020-10-27 15:20:16
    201027.TXT     2020-10-27 23:56:10 32912
    201028.TXT     2020-10-28 09:16:12 36172
  049/           2020-10-27 15:46:02
  004/           2020-10-27 16:24:08
    201027.TXT     2020-10-27 23:44:08 10969
    201028.TXT     2020-10-28 09:28:08 9300
  201028.TXT     2020-10-28 09:36:00 4810
LOG.TXT        2020-10-28 09:37:42 711069
FIFO.BIN       2020-10-28 09:36:00 17307
FIDX.BIN       2020-10-27 15:30:06 4
TIME.TXT       2020-10-28 09:36:22 10

In the following loop no data was sent via 4G because that very first frame was not found and the whole subsequent frames in the FIFO were not sent, and the 4G network switched off.

In conclusion we need to add an intelligent check if the file exists. If it doesn't then move to the next frame in the FIFO (or LIFO)