Improved error messaging

[sebastian-fox]

In some cases where errors occur because of no data (for combinations of indicator and area type), the messaging isn't clear for the user

library(fingertipsR)

phof_data_live <- fingertips_data(ProfileID = 19, AreaTypeID = 202, rank=TRUE) 
test <- indicator_order(DomainID = 1000044, AreaTypeID = 202, ParentAreaTypeID = 6)