Don't write empty $content in tmpfile and return if tmpfile is empty

snippy

@@ -150,12 +150,19 @@ run() {
             content="$( bashdown_simple < "${snippets_directory}/${snippet}" )"
         fi
 
-        printf "%s" "$content" > "$tmpfile"
+        if [ -n "$content" ]; then
+            printf "%s" "$content" > "$tmpfile"
+        fi
 
     else [[ ${snippet} =~ ^$ ]]
         ${snippet##*$} 2>/dev/null > "$tmpfile" # execute as bashcommand
     fi
 
+    # if tmpfile is empty at this step, nothing to do.
+    if [ ! -s "$tmpfile" ]; then
+        return
+    fi
+
     # save current clipboard
     current_clipboard=$(xsel -b)
     # replace {clipboard} by the clipboard content