population scaling with no matching names silently returns only NAs

[dsweber2]

using e.g. this step

    preproc %<>% step_population_scaling(
      all_numeric(),
      df = state_census,
      df_pop_col = "pop",
      create_new = FALSE,
      rate_rescaling = 1e5,
      by = c("geo_value" = "abbr")
    )

with this "data"

constant <- as_epi_archive(tibble(
  geo_value = "g1",
  time_value = seq(as.Date("2012-01-01"), by = "day", length.out = 90),
  version = seq(as.Date("2012-01-01"), by = "day", length.out = 90),
  a = 25
))

is happily passed on to lm.fit, which then sees no data to fit on. Would probably be good to error out if there are columns in the dataset that aren't in df_pop_col.