Revert "frequencyQuery: stop with error if vc is empty"

This reverts commit 4a89dc4675d596217593e375aae5972f7caf8a73.

Reason for revert: Missing pipe, rather needs a filter

Change-Id: I5c6f7b2150d7ee4457a55858dfb0f48a0965bfb4
diff --git a/R/KorAPQuery.R b/R/KorAPQuery.R
index 5ba459b..cf848f0 100644
--- a/R/KorAPQuery.R
+++ b/R/KorAPQuery.R
@@ -346,7 +346,6 @@
         corpusQuery(kco, query, vc, metadataOnly = TRUE, as.df = TRUE, ...) %>%
         mutate(total = corpusStats(kco, vc=vc, as.df=TRUE)$tokens)
       } ) %>%
-      { if (.$total == 0)  stop(paste0("Virtual corpus \"",vc, "\" is empty. Cannot calculate relative frequencies."), call. = FALSE) }
       ci(conf.level = conf.level)
 })