This function returns true under the following conditions:
no time series: ncol(monitor$data) == 1
no time series records: nrow(monitor$data) == 0
all timeseries values are NA
This makes for more readable code in functions that need to test for this.
monitor_isEmpty(monitor)
mts_monitor object
Invisibly returns TRUE
if no data exist in mts_monitor
, FALSE
otherwise.