wgl: Make context not current before deleting it.

dlls/opengl32/tests/opengl.c

@@ -552,6 +552,11 @@ static void test_deletecontext(HDC hdc)
 
     res = wglDeleteContext(hglrc);
     ok(res == TRUE, "wglDeleteContext failed\n");
+
+    /* WGL makes a context not current when deleting it. This differs from GLX behavior where
+     * deletion takes place when the thread becomes not current. */
+    hglrc = wglGetCurrentContext();
+    ok(hglrc == NULL, "A WGL context is active while none was expected\n");
 }
 
 static void test_make_current_read(HDC hdc)

dlls/winex11.drv/opengl.c

@@ -1783,6 +1783,10 @@ BOOL CDECL X11DRV_wglDeleteContext(HGLRC hglrc)
         return FALSE;
     }
 
+    /* WGL makes a context not current if it is active before deletion. GLX waits until the context is not current. */
+    if (ctx == NtCurrentTeb()->glContext)
+        wglMakeCurrent(ctx->hdc, NULL);
+
     if (ctx->ctx)
     {
         wine_tsx11_lock();