Fix line-between broking when file start with comment

Issue 525

Author: mariovalney

src/options/lines-between-rulesets.js

@@ -236,6 +236,10 @@ let option = {
       if (this.prevLineIsComment(node, index) || this.isComment(prevChild)) {
         let lastNonCommentIndex = this.findLatestNonCommentNode(node, index);
         prevChild = node.get(lastNonCommentIndex);
+
+        if (!prevChild) {
+          return;
+        }
       }
 
       if (prevChild.is('space')) {

test/options/lines-between-rulesets/process/css/2-lines-between-rulesets.expected.css

@@ -1,3 +1,4 @@
+/*comment*/
 .foo {background: red;}
 
 

test/options/lines-between-rulesets/process/css/lines-between-rulesets.css

@@ -1 +1,2 @@
+/*comment*/
 .foo {background: red;}/*comment*/.bar{border: 1px solid red;}.baz{color: #fff;}

test/options/lines-between-rulesets/process/css/lines-between-rulesets.expected.css

@@ -1,3 +1,4 @@
+/*comment*/
 .foo {background: red;}
 
 /*comment*/.bar{border: 1px solid red;}