🐛 Initialize active editor state correctly after reload

Fixes the following bug:

1. Open Atom
2. Open a file
3. Observe the file's encoding in the status bar
4. Reload Atom
5. Close the file
6. Observe that the closed file's encoding is still present in the
status bar

This bug occured because the reload did not deserialize/serialze the
workspace's active text editor state. As a result, when closing the
text editor in step 5, we failed to notify observers that there is no
longer an active text editor.

spec/workspace-spec.js

@@ -120,6 +120,20 @@ describe('Workspace', () => {
         expect(atom.workspace.getTextEditors().length).toBe(0)
       })
     })
+
+    it('remembers whether the workspace had an active text editor', async () => {
+      await atom.workspace.open('../sample.txt')
+      expect(atom.workspace.hasActiveTextEditor).toBe(true)
+
+      simulateReload()
+      expect(atom.workspace.hasActiveTextEditor).toBe(true)
+
+      atom.workspace.getActivePane().destroy()
+      expect(atom.workspace.hasActiveTextEditor).toBe(false)
+
+      simulateReload()
+      expect(atom.workspace.hasActiveTextEditor).toBe(false)
+    })
   })
 
   describe('::open(itemOrURI, options)', () => {

src/workspace.js

@@ -216,7 +216,7 @@ module.exports = class Workspace extends Model {
       bottom: this.createDock('bottom')
     }
     this.activePaneContainer = this.paneContainers.center
-    this.activeTextEditor = null
+    this.hasActiveTextEditor = false
 
     this.panelContainers = {
       top: new PanelContainer({viewRegistry: this.viewRegistry, location: 'top'}),
@@ -345,7 +345,8 @@ module.exports = class Workspace extends Model {
         left: this.paneContainers.left.serialize(),
         right: this.paneContainers.right.serialize(),
         bottom: this.paneContainers.bottom.serialize()
-      }
+      },
+      hasActiveTextEditor: this.hasActiveTextEditor
     }
   }
 
@@ -372,6 +373,10 @@ module.exports = class Workspace extends Model {
       this.paneContainers.center.deserialize(state.paneContainer, deserializerManager)
     }
 
+    if (state.hasActiveTextEditor != null) {
+      this.hasActiveTextEditor = state.hasActiveTextEditor
+    }
+
     this.updateWindowTitle()
   }
 
@@ -425,12 +430,11 @@ module.exports = class Workspace extends Model {
     }
 
     if (paneContainer === this.getCenter()) {
-      const newActiveTextEditor = (item instanceof TextEditor) ? item : null
-      const oldActiveTextEditor = this.activeTextEditor
+      const hadActiveTextEditor = this.hasActiveTextEditor
+      this.hasActiveTextEditor = item instanceof TextEditor
 
-      if (newActiveTextEditor || oldActiveTextEditor) {
-        this.activeTextEditor = newActiveTextEditor
-        const itemValue = (this.activeTextEditor || undefined)
+      if (this.hasActiveTextEditor || hadActiveTextEditor) {
+        const itemValue = this.hasActiveTextEditor ? item : undefined
         this.emitter.emit('did-change-active-text-editor', itemValue)
       }
     }