Don't throw when ::getDefaultCharacterWidth is called while detached

spec/text-editor-element-spec.coffee

@@ -147,9 +147,9 @@ describe "TextEditorElement", ->
       expect(element.shadowRoot.textContent).toContain "goodbye"
 
   describe "::getDefaultCharacterWidth", ->
-    it "throws an exception if the editor is not attached", ->
+    it "returns null before the element is attached", ->
       element = new TextEditorElement
-      expect(-> element.getDefaultCharacterWidth()).toThrow("The editor must be attached to get the default character width")
+      expect(element.getDefaultCharacterWidth()).toBeNull()
 
     it "returns the width of a character in the root scope", ->
       element = new TextEditorElement

src/text-editor-element.coffee

@@ -60,7 +60,6 @@ class TextEditorElement extends HTMLElement
     @__spacePenView = new TextEditorView(this)
 
   attachedCallback: ->
-    @attached = true
     @buildModel() unless @getModel()?
     @mountComponent() unless @component?.isMounted()
     @component.checkForVisibilityChange()
@@ -68,7 +67,6 @@ class TextEditorElement extends HTMLElement
     @emitter.emit("did-attach")
 
   detachedCallback: ->
-    @attached = false
     @emitter.emit("did-detach")
 
   initialize: (model) ->
@@ -173,7 +171,6 @@ class TextEditorElement extends HTMLElement
   #
   # Returns a {Number} of pixels.
   getDefaultCharacterWidth: ->
-    throw new Error("The editor must be attached to get the default character width") unless @attached
     @getModel().getDefaultCharWidth()
 
   # Extended: call the given `callback` when the editor is attached to the DOM.