Fix KSS parser failing on empty file

lib/modules/kss-parser.js

@@ -1,4 +1,3 @@
-
 'use strict';
 var kss = require('kss'),
   path = require('path'),
@@ -94,6 +93,10 @@ function processBlock(block, options) {
 }
 
 function processFile(contents, filePath, syntax, options) {
+  if (!contents || contents.length === 0) {
+    return Q.resolve([]);
+  }
+
   return Q.Promise(function(resolve, reject) {
     var blockPromises = [],
         blocks;

test/unit/modules/kss-parser.test.js

@@ -19,6 +19,27 @@ describe('KSS parser', function() {
     };
   }
 
+  it('does not crash on empty .less file', function(done) {
+    var files = { 'file1.less': '' };
+    parse(files).then(function(sections) {
+      expect(sections.length).to.eql(0);
+    }).then(done).catch(done);
+  });
+
+  it('does not crash on empty .sass file', function(done) {
+    var files = { 'file1.sass': '' };
+    parse(files).then(function(sections) {
+      expect(sections.length).to.eql(0);
+    }).then(done).catch(done);
+  });
+
+  it('does not crash on empty .scss file', function(done) {
+    var files = { 'file1.scss': '' };
+    parse(files).then(function(sections) {
+      expect(sections.length).to.eql(0);
+    }).then(done).catch(done);
+  });
+
   it('parses sections from multiple files', function(done) {
     var files = {
       'file1.less': multiline(function() {