Fix bug in utf16_to_utf8 for zero length strings

This fixes the behavior of sending EOF by pressing Ctrl+Z => Enter in a
windows console.

Previously, that would trip the unpaired surrogate error, whereas now we
correctly detect EOF.

1 files changed, 6 insertions, 0 deletions

diff --git a/library/std/src/sys/windows/stdio/tests.rs b/library/std/src/sys/windows/stdio/tests.rs
new file mode 100644
index 00000000000..1e53e0bee63
--- /dev/null
+++ b/library/std/src/sys/windows/stdio/tests.rs
@@ -0,0 +1,6 @@
+use super::utf16_to_utf8;
+
+#[test]
+fn zero_size_read() {
+    assert_eq!(utf16_to_utf8(&[], &mut []).unwrap(), 0);
+}