Incorrect calls to strlen in CFE_ES_TaskInit

[jphickey]

Describe the bug
The function calls strlen as:
strlen(EventBuffer-1)

To Reproduce
This is undefined behavior but probably works by accident most of the time, so long as the byte before EventBuffer is not null. This also generates a compiler warning which somehow was never noticed before in previous reviews of this code (gcc 7.4.0 with -Wall switch)

Expected behavior
It probably was meant to be:
strlen(EventBuffer)-1

System observed on:
Ubuntu 18.04 (64-bit), kernel 5.0.0-23-generic, gcc 7.4.0-1ubuntu1~18.04.1

Reporter Info
Joe Hickey

[jphickey]

Note: Although the sample config does use -Wall by default, it appears GCC can only trigger this warning if also using -O2 or above, which is probably why it wasn't noticed in previous reviews/verification.