Allow non-existent files to be opened from fuzzy finder

The previous isFileSync check prevented unsaved buffers with a path to a
non-existent file from being opened from the fuzzy finder.

Now an error is only displayed if the selected path is a directory.

Closes #686

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

@@ -98,13 +98,13 @@ class FuzzyFinderView extends SelectList
   confirmed : ({filePath}) ->
     return unless filePath
 
-    if fsUtils.isFileSync(filePath)
+    if fsUtils.isDirectorySync(filePath)
+      @setError('Selected path is a directory')
+      setTimeout((=> @setError()), 2000)
+    else
       lineNumber = @getLineNumber()
       @cancel()
       @openPath(filePath, lineNumber)
-    else
-      @setError('Selected path does not exist')
-      setTimeout((=> @setError()), 2000)
 
   toggleFileFinder: ->
     @finderMode = 'file'

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

@@ -109,12 +109,12 @@ describe 'FuzzyFinder', ->
         expect(editor2.getPath()).toBe expectedPath
         expect(editor2.isFocused).toBeTruthy()
 
-      describe "when the selected path isn't a file that exists", ->
+      describe "when the selected path is a directory", ->
         it "leaves the the tree view open, doesn't open the path in the editor, and displays an error", ->
           rootView.attachToDom()
           editorPath = rootView.getActiveView().getPath()
           rootView.trigger 'fuzzy-finder:toggle-file-finder'
-          finderView.confirmed({filePath: 'dir/this/is/not/a/file.txt'})
+          finderView.confirmed({filePath: project.resolve('dir')})
           expect(finderView.hasParent()).toBeTruthy()
           expect(rootView.getActiveView().getPath()).toBe editorPath
           expect(finderView.error.text().length).toBeGreaterThan 0