Only open paths that are files that exist

The filesystem may have changed while the fuzzy finder
is open or since the last time the paths were loaded so
don't try to open paths unless they are files that
currently exist when confirmed.

src/packages/fuzzy-finder/spec/fuzzy-finder-spec.coffee

@@ -86,6 +86,18 @@ describe 'FuzzyFinder', ->
         expect(editor2.getPath()).toBe expectedPath
         expect(editor2.isFocused).toBeTruthy()
 
+      describe "when the selected path isn't a file that exists", ->
+        it "leaves the the tree view open, doesn't open the path in the editor, and displays an error", ->
+          rootView.attachToDom()
+          path = rootView.getActiveEditor().getPath()
+          rootView.trigger 'fuzzy-finder:toggle-file-finder'
+          finder.confirmed('dir/this/is/not/a/file.txt')
+          expect(finder.hasParent()).toBeTruthy()
+          expect(rootView.getActiveEditor().getPath()).toBe path
+          expect(finder.find('.error').text().length).toBeGreaterThan 0
+          advanceClock(2000)
+          expect(finder.find('.error').text().length).toBe 0
+
   describe "buffer-finder behavior", ->
     describe "toggling", ->
       describe "when the active editor contains edit sessions for buffers with paths", ->

src/packages/fuzzy-finder/src/fuzzy-finder.coffee

@@ -65,8 +65,12 @@ class FuzzyFinder extends SelectList
 
   confirmed : (path) ->
     return unless path.length
-    @cancel()
-    @openPath(path)
+    if fs.isFile(rootView.project.resolve(path))
+      @cancel()
+      @openPath(path)
+    else
+      @setError('Selected path does not exist')
+      setTimeout(=> @setError('')), 2000
 
   cancelled: ->
     @miniEditor.setText('')