Fix random signature

canvas.js

@@ -138,7 +138,7 @@ document.getElementById('randomize').onclick = function(e) {
   randomElement('input[name="font"]').checked = true;
   randomElement('input[name="icon"]').checked = true;
   document.getElementById('step2value').value = document.getElementById('step2value').innerText = sampleTexts[Math.trunc(Math.random() * sampleTexts.length)];
-  if (document.getElementById('signature').value.match(/\t$/))
+  if (document.getElementById('signature').value.match(/(\t$|^$)/))
     document.getElementById('signature').value = sampleSignatures[Math.trunc(Math.random() * sampleSignatures.length)];
   draw();
 }