fix missing fields for json, ek and pdml when used with -e fields

fix missing fields for json, ek and pdml when used with -e fields

Description:

when -T json,ed or pdml used in conjunction with -e fields they would
always miss  the last field.

in case of json and ek, if some fields in the middle are empty,
the generated json would be invalid.

sample for ek:

 {  "_index": "packets-2016-06-30",  "_type": "pcap_file",
 "_score": null,  "_source":
 {  "layers": {  "e212.mcc": ["255","262"]  "frame.time_epoch":
 ["1426550400.004751510"],  "e212.mnc": ["1","1"]  }  }  }

command:

tshark -T ek -r C:\a.pcap -e e212.mcc -e frame.comment
-e frame.time_epoch -e e212.mnc > C:\test.json

note:

the comma is missing between e212.mcc and frame.time_epoch

Change-Id: I2efae0c48036cf6313e2a064453c8dbc49f38b09
Reviewed-on: https://code.wireshark.org/review/16226
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Martin Kacer <kacer.martin@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>