Win32: Fix key name code changing global key state

This prevents glfwInit from potentially clobbering the dead key state
for other applications.

Closes #2018

CONTRIBUTORS.md

@@ -10,6 +10,7 @@ video tutorials.
  - Matt Arsenault
  - ashishgamedev
  - David Avedissian
+ - Luca Bacci
  - Keith Bauer
  - John Bartholomew
  - Coşku Baş

README.md

@@ -205,6 +205,8 @@ information on what to include when reporting a bug.
  - [Win32] Bugfix: Content scale queries could fail silently (#1615)
  - [Win32] Bugfix: Content scales could have garbage values if monitor was recently
    disconnected (#1615)
+ - [Win32] Bugfix: Key name update modified global key state on Windows 10 1607
+   and later (#2018)
  - [Cocoa] Added support for `VK_EXT_metal_surface` (#1619)
  - [Cocoa] Added locating the Vulkan loader at runtime in an application bundle
  - [Cocoa] Moved main menu creation to GLFW initialization time (#1649)

src/win32_init.c

@@ -458,6 +458,11 @@ void _glfwUpdateKeyNamesWin32(void)
 {
     int key;
     BYTE state[256] = {0};
+    UINT flags = 0;
+
+    // Avoid modifying the global key state if supported
+    if (_glfwIsWindows10AnniversaryUpdateOrGreaterWin32())
+        flags = (1 << 2);
 
     memset(_glfw.win32.keynames, 0, sizeof(_glfw.win32.keynames));
 
@@ -487,13 +492,13 @@ void _glfwUpdateKeyNamesWin32(void)
 
         length = ToUnicode(vk, scancode, state,
                            chars, sizeof(chars) / sizeof(WCHAR),
-                           0);
+                           flags);
 
         if (length == -1)
         {
             length = ToUnicode(vk, scancode, state,
                                chars, sizeof(chars) / sizeof(WCHAR),
-                               0);
+                               flags);
         }
 
         if (length < 1)