Make Err_win_error return English messages

English messages are hopefully strictly ASCII. Passing 0 as language id
may return a non-English message using the current code page and
resulting in invalid UTF-8.

See LUCY-311.
diff --git a/runtime/core/Clownfish/Err.c b/runtime/core/Clownfish/Err.c
index 82daf02..7ca59b8 100644
--- a/runtime/core/Clownfish/Err.c
+++ b/runtime/core/Clownfish/Err.c
@@ -254,7 +254,8 @@
     DWORD message_len = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM,
                                       NULL,       // message source table
                                       GetLastError(),
-                                      0,          // language id
+                                      MAKELANGID(LANG_ENGLISH,
+                                                 SUBLANG_ENGLISH_US),
                                       buf,
                                       buf_size,
                                       NULL        // empty va_list