Assign cachedDiskContents when unsaved buffer is deserialized

This allows the buffer to return to an "unmodified" state if the
unsaved changes are reversed.

spec/app/text-buffer-spec.coffee

@@ -1251,11 +1251,14 @@ describe 'Buffer', ->
     describe "when the serialized buffer had unsaved changes", ->
       it "restores the previous unsaved state of the buffer", ->
         path = buffer.getPath()
+        previousText = buffer.getText()
         buffer.setText("abc")
         reloadBuffer()
         expect(serializedState.text).toBe "abc"
         expect(buffer.getPath()).toBe(path)
         expect(buffer.getText()).toBe("abc")
+        buffer.setText(previousText)
+        expect(buffer.isModified()).toBeFalsy()
 
     describe "when the serialized buffer was unsaved and had no path", ->
       it "restores the previous unsaved state of the buffer", ->

src/app/text-buffer.coffee

@@ -41,11 +41,13 @@ class Buffer
       @setPath(path)
       if initialText?
         @setText(initialText)
+        @updateCachedDiskContents()
       else
         @reload()
     else
       @setText(initialText ? '')
 
+
     @undoManager = new UndoManager(this)
 
   destroy: ->