Fix endless event loop in Haiku

SDL for Haiku always send a WM size change at init. We did catch that it
would not cause any SDL mode set, so we ignored it, but we forgot to
reset the resize width and height. So each run of the event loop would
try to resize the window again and again to the same size.

Thanks to event throttling this was not very noticeable, the main
consequence was that some stuff was reset and for example the tooltips
in the status bar were not showing at all.

src/graph.c

@@ -325,7 +325,12 @@ try_again:
   pixels_changed = (Pixel_ratio!=pix_ratio);
   
   if (!screen_changed && !pixels_changed)
+  {
+    Resize_width=0;
+    Resize_height=0;
     return 0;
+  }
+
   if (screen_changed)
   {
     Set_mode_SDL(&width, &height,fullscreen);