FIX: poll builder should ignore empty lines

Although pollOptionsCount skips empty lines, pollOutput inserts empty
lines. Skip them instead.

Signed-off-by: Loic Dachary <loic@dachary.org>

plugins/poll/test/javascripts/controllers/poll-ui-builder-test.js.es6

@@ -210,7 +210,7 @@ test("multiple pollOutput", function() {
     isMultiple: true,
     pollType: controller.get("multiplePollType"),
     pollMin: 1,
-    pollOptions: "1\n2"
+    pollOptions: "\n\n1\n\n2"
   });
 
   equal(controller.get("pollOutput"), "[poll type=multiple min=1 max=2]\n* 1\n* 2\n[/poll]", "it should return the right output");