Only restore window when it is minimized

Restoring a maximized windows on Windows unmaximizes it.

Closes #3381

src/browser/atom-application.coffee

@@ -345,7 +345,7 @@ class AtomApplication
     if existingWindow?
       openedWindow = existingWindow
       openedWindow.openPath(pathToOpen, initialLine)
-      openedWindow.restore()
+      openedWindow.restore() if openedWindow.isMinimized()
     else
       if devMode
         try

src/browser/atom-window.coffee

@@ -173,6 +173,8 @@ class AtomWindow
 
   isFocused: -> @browserWindow.isFocused()
 
+  isMinimized: -> @browserWindow.isMinimized()
+
   isWebViewFocused: -> @browserWindow.isWebViewFocused()
 
   isSpecWindow: -> @isSpec