Don't send mail if no text was generated

run.sh

@@ -24,6 +24,13 @@ function preview {
     echo ""
 }
 
+PREVIEW_TEXT="$(preview)"
+
+if [ -z "${PREVIEW_TEXT}" ]
+then
+    (>&2 echo "nothing to send")
+    exit 0
+fi
 
 (cat << EOF
 Subject: Programm-Info-Bot