Add Buffer.isEmpty()

To be used by Buffer.isModified() for when the
buffer has no backing file

spec/app/buffer-spec.coffee

@@ -650,3 +650,16 @@ describe 'Buffer', ->
       expect(buffer.usesSoftTabs()).toBeFalsy()
       buffer.setText("")
       expect(buffer.usesSoftTabs()).toBeUndefined()
+
+  describe ".isEmpty()", ->
+    it "returns true for an empty buffer", ->
+      buffer.setText('')
+      expect(buffer.isEmpty()).toBeTruthy()
+
+    it "returns false for a non-empty buffer", ->
+      buffer.setText('a')
+      expect(buffer.isEmpty()).toBeFalsy()
+      buffer.setText('a\nb\nc')
+      expect(buffer.isEmpty()).toBeFalsy()
+      buffer.setText('\n')
+      expect(buffer.isEmpty()).toBeFalsy()

src/app/buffer.coffee

@@ -244,10 +244,12 @@ class Buffer
     if @file
       @memoryContentSignature != @diskContentSignature
     else
-      @lines.length > 1 or @lines[0]
+      not @isEmpty()
 
   isInConflict: -> @conflict
 
+  isEmpty: -> @lines.length is 1 and @lines[0].length is 0
+
   getAnchors: -> new Array(@anchors...)
 
   addAnchor: (options) ->