Ensure we never deserialize two instances of the same buffer

We might have two edit sessions pointing to the same buffer, for
example if we have a split pane… So when we deserialize a buffer, we
always need to check that we don't already have an instance of that
buffer on the project. If we do, then we've already deserialized it
once so we don't need to worry about the saved text.

We still have a problem when deserializing previously unsaved buffers,
because we can't use the path to identify them.

spec/app/text-buffer-spec.coffee

@@ -1265,3 +1265,9 @@ describe 'Buffer', ->
         expect(serializedState.path).toBeUndefined()
         expect(buffer.getPath()).toBeUndefined()
         expect(buffer.getText()).toBe("abc")
+
+    it "never deserializes two separate instances of the same buffer", ->
+      serializedState = buffer.serialize()
+      buffer.release()
+      buffer = Buffer.deserialize(serializedState)
+      expect(Buffer.deserialize(serializedState)).toBe buffer

src/app/project.coffee

@@ -127,19 +127,17 @@ class Project
     else
       @on 'buffer-created', (buffer) -> callback(buffer)
 
-  bufferForPath: (filePath) ->
+  bufferForPath: (filePath, text) ->
     if filePath?
       filePath = @resolve(filePath)
       if filePath
         buffer = _.find @buffers, (buffer) -> buffer.getPath() == filePath
-        buffer or @buildBuffer(filePath)
-      else
-
+        buffer or @buildBuffer(filePath, text)
     else
-      @buildBuffer()
+      @buildBuffer(null, text)
 
-  buildBuffer: (filePath) ->
-    buffer = new Buffer(filePath)
+  buildBuffer: (filePath, text) ->
+    buffer = new Buffer(filePath, text)
     @buffers.push buffer
     @trigger 'buffer-created', buffer
     buffer

src/app/text-buffer.coffee

@@ -25,11 +25,8 @@ class Buffer
   invalidMarkers: null
   refcount: 0
 
-  @deserialize: (state) ->
-    if state && (state.path? || state.text?)
-      new Buffer(state.path, state.text)
-    else
-      new Buffer(null)
+  @deserialize: ({path, text}) ->
+    project.bufferForPath(path, text)
 
   constructor: (path, initialText) ->
     @id = @constructor.idCounter++