Only reset font size if font size has been changed

spec/workspace-spec.coffee

@@ -425,6 +425,7 @@ describe "Workspace", ->
       expect(atom.config.get('editor.fontSize')).toBe 1
       workspace.decreaseFontSize()
       expect(atom.config.get('editor.fontSize')).toBe 1
+
   describe "::resetFontSize()", ->
     it "resets the font size to the window's starting font size", ->
       originalFontSize = 6
@@ -439,6 +440,13 @@ describe "Workspace", ->
       workspace.resetFontSize()
       expect(atom.config.get('editor.fontSize')).toBe originalFontSize
 
+    it "does nothing if the font size has not been changed", ->
+      originalFontSize = 6
+
+      atom.config.set('editor.fontSize', originalFontSize)
+      workspace.resetFontSize()
+      expect(atom.config.get('editor.fontSize')).toBe originalFontSize
+
   describe "::openLicense()", ->
     it "opens the license as plain-text in a buffer", ->
       waitsForPromise -> workspace.openLicense()

src/workspace.coffee

@@ -623,7 +623,8 @@ class Workspace extends Model
 
   # Restore to the window's original editor font size.
   resetFontSize: ->
-    atom.config.set("editor.fontSize", @originalFontSize)
+    if @originalFontSize
+      atom.config.set("editor.fontSize", @originalFontSize)
 
   # Removes the item's uri from the list of potential items to reopen.
   itemOpened: (item) ->