Win32: Fix invalid hat bit mask being accepted

It is reportedly possible to get opposing directions of an XInput DPad
bit mask set simultaneously with some controllers.

This commit ensures that those values are not passed on to other parts
of GLFW.

This commit is based on the PR #2291 by @ PeterJohnson but with the
following changes:
 - moved XInput-specific special case to XInput implementation
 - attempt to preserve data by only masking out the invalid axis
 - admin (credit, changelog, commit message)

Closes #2291

CONTRIBUTORS.md

@@ -102,6 +102,7 @@ video tutorials.
  - JannikGM
  - Erik S. V. Jansson
  - jjYBdx4IL
+ - Peter Johnson
  - Toni Jovanoski
  - Arseny Kapoulkine
  - Cem Karan

README.md

@@ -232,6 +232,7 @@ information on what to include when reporting a bug.
  - [Win32] Bugfix: Right shift emitted `GLFW_KEY_UNKNOWN` when using a CJK IME (#2050)
  - [Win32] Bugfix: `glfwWaitEventsTimeout` did not return for some sent messages (#2408)
  - [Win32] Bugfix: Fix pkg-config for dynamic library on Windows (#2386, #2420)
+ - [Win32] Bugfix: XInput could reportedly provide invalid DPad bit masks (#2291)
  - [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_joystick.c

@@ -736,6 +736,13 @@ GLFWbool _glfwPollJoystickWin32(_GLFWjoystick* js, int mode)
         if (xis.Gamepad.wButtons & XINPUT_GAMEPAD_DPAD_LEFT)
             dpad |= GLFW_HAT_LEFT;
 
+        // Treat invalid combinations as neither being pressed
+        // while preserving what data can be preserved
+        if ((dpad & GLFW_HAT_RIGHT) && (dpad & GLFW_HAT_LEFT))
+            dpad &= ~(GLFW_HAT_RIGHT | GLFW_HAT_LEFT);
+        if ((dpad & GLFW_HAT_UP) && (dpad & GLFW_HAT_DOWN))
+            dpad &= ~(GLFW_HAT_UP | GLFW_HAT_DOWN);
+
         _glfwInputJoystickHat(js, 0, dpad);
     }