Fix mismatch with spec on condition to write/read lfnst_idx after !1106

lfnst_idx shall be parsed when IntraSubPartitionsSplitType ==
ISP_NO_SPLIT, whereas the opposite is done currently.
7 jobs for !1119 with fix-lfnst_idx-parsing in 10 minutes and 14 seconds (queued for 5 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #3699
macos
build_macos

00:02:57

passed #3700
ubuntu1604
build_ubuntu1604

00:07:44

passed #3701
ubuntu1804
build_ubuntu1804

00:05:33

passed #3702
ubuntu1804-gcc8
build_ubuntu1804-gcc8

00:05:17

passed #3703
vc1900
build_vc1900

00:07:35

passed #3704
vc191x
build_vc191x

00:08:30

passed #3705
vc192x
build_vc192x

00:08:13