Fix IO::FileDescriptor.new for closed fd

spec/std/io/file_descriptor_spec.cr

@@ -14,6 +14,17 @@ private def shell_command(command)
 end
 
 describe IO::FileDescriptor do
+  describe "#initialize" do
+    it "handles closed file descriptor gracefully" do
+      a, b = IO.pipe
+      a.close
+      b.close
+
+      fd = IO::FileDescriptor.new(a.fd)
+      fd.closed?.should be_true
+    end
+  end
+
   it "reopen STDIN with the right mode", tags: %w[slow] do
     code = %q(puts "#{STDIN.blocking} #{STDIN.info.type}")
     compile_source(code) do |binpath|

src/crystal/system/win32/file_descriptor.cr

@@ -92,8 +92,19 @@ module Crystal::System::FileDescriptor
     raise NotImplementedError.new("Crystal::System::FileDescriptor#system_close_on_exec=") if close_on_exec
   end
 
-  private def system_closed?
-    false
+  private def system_closed? : Bool
+    file_type = LibC.GetFileType(windows_handle)
+
+    if file_type == LibC::FILE_TYPE_UNKNOWN
+      case error = WinError.value
+      when .error_invalid_handle?
+        return true
+      else
+        raise IO::Error.from_os_error("Unable to get info", error, target: self)
+      end
+    else
+      false
+    end
   end
 
   def self.fcntl(fd, cmd, arg = 0)

src/io/file_descriptor.cr

@@ -41,8 +41,13 @@ class IO::FileDescriptor < IO
 
   def initialize(fd : Handle, blocking = nil, *, @close_on_finalize = true)
     @volatile_fd = Atomic.new(fd)
+    @closed = true # This is necessary so we can reference `self` in `system_closed?` (in case of an exception)
+
+    # TODO: Refactor to avoid calling `GetFileType` twice on Windows (once in `system_closed?` and once in `system_info`)
     @closed = system_closed?
 
+    return if @closed
+
     if blocking.nil?
       blocking =
         case system_info.type