more helpful error message for inappropriate value of nThin

[johnrbryant]

fetchSummary(filename)
Error in foldMCMCList(mcmc.list.i) : 'l' has fewer than 2 rows
traceback()
7: stop(gettextf("'%s' has fewer than %d rows", "l", 2L))
6: foldMCMCList(mcmc.list.i)
5: makeGelmanDiag(object = object, filename = filename)
4: .local(object, ...)
3: summary(object = object, filename = filename)
2: summary(object = object, filename = filename)
1: fetchSummary(filename)

model <- Model(y ~ Poisson(mean ~ (age + talb18),
useExpose = FALSE))

dataModels <- list(Model(cen_ins ~ Poisson(mean ~ (talb18+age))),
Model(idi_ins ~ Poisson(mean ~ (talb18+age))))

pop <- cen_ins %>%
collapseDimension("year") %>%
addDimension(name = "year", labels = 2014:2019, dimscale = "Intervals")

pop <- pop+1 %>%
round(0)

datasets <- list(idi_ins = idi_ins, cen_ins = cen_ins)
filename <- "output 23-7 v2"

estimateCounts(y = pop,
model=model,
datasets=datasets,
dataModels=dataModels,
filename = filename,
exposure = NULL,
nBurnin = 1000,
nSim = 1000,
nThin = 1000,
nChain = 3)

Maybe have rule for what constitutes an unlikely nThin?