FIX: Infinite loop when poll step is zero (#5380)

* Fix infinite loop when poll step is zero

* Add test for step minimum and for breaking test

* Remove trailing spaces (eslint)

* Remove extra space (eslint)

* Removed test call .twice

plugins/poll/assets/javascripts/lib/discourse-markdown/poll.js.es6

@@ -133,6 +133,11 @@ const rule = {
     let max = parseInt(attrs["max"], 10);
     let step = parseInt(attrs["step"], 10);
 
+    // infinite loop if step < 1
+    if (step < 1) {
+      step = 1;
+    }
+
     let header = [];
 
     let token = new state.Token('poll_open', 'div', 1);