Fix issue with the undefined offset in JSON array when new instance is added
Fix issue with the undefined offset in JSON array when new instance is added

Signed-off-by: Roman Ondráček <f226ca4e9e6347db373d27b729024cc130f78ec9@iqrf.com>

iqrfsdk/iqrf-daemon-webapp,iqrfsdk/iqrf-daemon-webapp,iqrfsdk/iqrf-daemon-webapp,iqrfsdk/iqrf-daemon-webapp,iqrfsdk/iqrf-daemon-webapp