win32: Fix a handle leak in rb_w32_read_internal

One of its early returns after `setup_overlapped` did not close the event.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ext/-test-/win32/handle_count/depend

@@ -0,0 +1 @@
+handle_count.o: $(ruby_headers) $(hdrdir)/ruby/win32.h

ext/-test-/win32/handle_count/extconf.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: false
+if $mingw or $mswin
+  create_makefile("-test-/win32/handle_count")
+end

ext/-test-/win32/handle_count/handle_count.c

@@ -0,0 +1,16 @@
+#include <ruby.h>
+
+static VALUE
+handle_count(VALUE self)
+{
+    DWORD count;
+    if (!GetProcessHandleCount(GetCurrentProcess(), &count)) rb_sys_fail("GetProcessHandleCount");
+    return ULONG2NUM(count);
+}
+
+void
+Init_handle_count(void)
+{
+    VALUE m = rb_define_module_under(rb_define_module("Bug"), "Win32");
+    rb_define_module_function(m, "handle_count", handle_count, 0);
+}

test/-ext-/win32/test_handle_count.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: false
+require 'test/unit'
+
+module Bug
+  module Win32
+    class TestHandleCount < Test::Unit::TestCase
+      def test_read_nonblock_on_empty_pipe
+        require '-test-/win32/handle_count'
+        IO.pipe do |r, w|
+          r.read_nonblock(1, exception: false)
+          before = Bug::Win32.handle_count
+          1000.times {r.read_nonblock(1, exception: false)}
+          assert_operator(Bug::Win32.handle_count - before, :<, 100)
+        end
+      end
+    end
+  end
+end if /mswin|mingw/ =~ RUBY_PLATFORM

win32/win32.c

@@ -7433,6 +7433,7 @@ rb_w32_read_internal(int fd, void *buf, size_t size, rb_off_t *offset)
         err = GetLastError();
         if (err == ERROR_NO_DATA && (_osfile(fd) & FPIPE)) {
             DWORD state;
+            CloseHandle(ol.hEvent);
             if (GetNamedPipeHandleState((HANDLE)_osfhnd(fd), &state, NULL, NULL, NULL, NULL, 0) && (state & PIPE_NOWAIT)) {
                 errno = EWOULDBLOCK;
             }