If syntax analysis gets to calling this function the command is surely not single line if, because the command SLIF is recognised by IsCommandIF.
The syntax of the command IF is presented in the syntax table before SLIF and therefore if the syntax analyser gets here it can not be SLIF.
The original function IsCommandThis could also do failing automatically,
but it is simpler just to fail after the function call, so this function
is just a bit of speedup.
peNODE ex_IsCommandSLIF(peXobject pEx,
pLineSyntax p,
int *piFailure
){