check_months: Check if all months are between -12 and 12 (previous and current december)
Description
Make sure that all the months specified in the (probably complex)
month specification to dcc are correct months, in the sense that
they range between -12 and 12. Further, return the earliest month
in the complete selection to decide if we need previous year
climate later on.
Usage
check_months(selection)
Arguments
selection
the month selection as vector, list, or nested
list
Value
a list with the earliest month and the result of the check
(logical)