Win32: Fix OSMesa library not being unloaded

(cherry picked from commit 10e9033a29)

README.md

@@ -130,6 +130,7 @@ information on what to include when reporting a bug.
  - [Win32] Bugfix: `GLFW_KEY_PAUSE` scancode from `glfwGetKeyScancode` did not
    match event scancode (#1993)
  - [Win32] Bugfix: Instance-local operations used executable instance (#469,#1296,#1395)
+ - [Win32] Bugfix: The OSMesa library was not unloaded on termination
  - [Cocoa] Bugfix: A connected Apple AirPlay would emit a useless error (#1791)
  - [Wayland] Added support for file path drop events (#2040)
  - [Wayland] Bugfix: `glfwSetClipboardString` would fail if set to result of

src/win32_init.c

@@ -610,6 +610,7 @@ void _glfwPlatformTerminate(void)
 
     _glfwTerminateWGL();
     _glfwTerminateEGL();
+    _glfwTerminateOSMesa();
 
     _glfwTerminateJoysticksWin32();