Don't capture whitespace group in comment patterns

This was causing corruption when uncommenting XML since the fact that
it was being captured was throwing off the index used into the match.

Closes atom/language-xml#3

spec/language-mode-spec.coffee

@@ -208,6 +208,20 @@ describe "LanguageMode", ->
         languageMode.toggleLineCommentsForBufferRows(0, 0)
         expect(buffer.lineForRow(0)).toBe "// @color: #4D926F;"
 
+  describe "xml", ->
+    beforeEach ->
+      editor = atom.project.openSync('sample.xml', autoIndent: false)
+      editor.setText("<!-- test -->")
+      {buffer, languageMode} = editor
+
+      waitsForPromise ->
+        atom.packages.activatePackage('language-xml')
+
+    describe "when uncommenting lines", ->
+      it "removes the leading whitespace from the comment end pattern match", ->
+        languageMode.toggleLineCommentsForBufferRows(0, 0)
+        expect(buffer.lineForRow(0)).toBe "test"
+
   describe "folding", ->
     beforeEach ->
       editor = atom.project.openSync('sample.js', autoIndent: false)

src/language-mode.coffee

@@ -39,13 +39,13 @@ class LanguageMode
     return unless commentStartString
 
     buffer = @editor.buffer
-    commentStartRegexString = _.escapeRegExp(commentStartString).replace(/(\s+)$/, '($1)?')
+    commentStartRegexString = _.escapeRegExp(commentStartString).replace(/(\s+)$/, '(?:$1)?')
     commentStartRegex = new OnigRegExp("^(\\s*)(#{commentStartRegexString})")
     shouldUncomment = commentStartRegex.test(buffer.lineForRow(start))
 
     if commentEndString
       if shouldUncomment
-        commentEndRegexString = _.escapeRegExp(commentEndString).replace(/^(\s+)/, '($1)?')
+        commentEndRegexString = _.escapeRegExp(commentEndString).replace(/^(\s+)/, '(?:$1)?')
         commentEndRegex = new OnigRegExp("(#{commentEndRegexString})(\\s*)$")
         startMatch =  commentStartRegex.search(buffer.lineForRow(start))
         endMatch = commentEndRegex.search(buffer.lineForRow(end))