Fix deceptive class when an error occurs

Consider the following scenario:
1. Turn on regex
2. Search for something simple in the file, eg "this"
3. has-results class appears as expected
4. Add an opening parenthesis to the find pattern
5. Find box is still green?!?!
Step 5 introduces contradicting information: a red error message yet a
green find box with the has-results class.

So now when we set an error message we make sure to remove the
has-results class and add the has-no-results class.

I'm also fairly certain that nulling a function is not a good idea, so I
removed that line.

Author: winstliu

lib/find-view.coffee

@@ -307,7 +307,6 @@ class FindView extends View
       atom.beep()
 
   markersUpdated: (@markers) =>
-    @findError = null
     @updateResultCounter()
     @updateReplaceEnablement()
 
@@ -342,6 +341,8 @@ class FindView extends View
     @descriptionLabel.text(infoMessage).removeClass('text-error')
 
   setErrorMessage: (errorMessage) ->
+    this.removeClass('has-results')
+    this.addClass('has-no-results')
     @descriptionLabel.text(errorMessage).addClass('text-error')
 
   clearMessage: ->