os: fix os.open_file/3 wb mode creation of text files containing crlf on Windows (#20101)

vlib/os/file.c.v

@@ -109,8 +109,7 @@ pub fn open_file(path string, mode string, options ...int) !File {
 	if fd == -1 {
 		return error(posix_get_error_msg(C.errno))
 	}
-	fdopen_mode := mode.replace('b', '')
-	cfile := C.fdopen(fd, &char(fdopen_mode.str))
+	cfile := C.fdopen(fd, &char(mode.str))
 	if isnil(cfile) {
 		return error('Failed to open or create file "${path}"')
 	}

vlib/os/file_test.v

@@ -450,3 +450,30 @@ fn test_open_file_on_chinese_windows() {
 		assert os.file_size('中文.txt') == 2
 	}
 }
+
+fn test_open_file_crlf_binary_mode() {
+	teststr := 'hello\r\n'
+	fname := 'text.txt'
+
+	mut wfile := os.open_file(fname, 'w', 0o666)!
+	wfile.write_string(teststr)!
+	wfile.close()
+
+	mut fcont_w := os.read_file(fname)!
+
+	os.rm(fname) or {}
+
+	mut wbfile := os.open_file(fname, 'wb', 0o666)!
+	wbfile.write_string(teststr)!
+	wbfile.close()
+
+	mut fcont_wb := os.read_file(fname)!
+
+	os.rm(fname) or {}
+
+	$if windows {
+		assert fcont_w != teststr
+	}
+
+	assert fcont_wb == teststr
+}