Always select textSigle in corpus queries

Resolves #24

Change-Id: Iba859868b3e21ad3fb3d840f92441e65369a2f86
diff --git a/R/KorAPQuery.R b/R/KorAPQuery.R
index adc4024..db5ad6f 100644
--- a/R/KorAPQuery.R
+++ b/R/KorAPQuery.R
@@ -185,6 +185,9 @@
       if (metadataOnly) {
         fields <- fields[!fields %in% contentFields]
       }
+      if (!"textSigle" %in% fields) {
+        fields <- c(fields, "textSigle")
+      }
       request <-
         paste0('?q=',
                url_encode(enc2utf8(query)),