Reset the keyboard state when launching a message box (thanks, Sean!). Otherwise, pressed keys get stuck. Fixes Bugzilla #2776.
diff --git a/src/video/SDL_video.c b/src/video/SDL_video.c
index dbc3094..2e168de 100644
--- a/src/video/SDL_video.c
+++ b/src/video/SDL_video.c
@@ -3418,6 +3418,7 @@ SDL_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
SDL_CaptureMouse(SDL_FALSE);
SDL_SetRelativeMouseMode(SDL_FALSE);
show_cursor_prev = SDL_ShowCursor(1);
+ SDL_ResetKeyboard();
if (!buttonid) {
buttonid = &dummybutton;