engine: bump MAXCLIPNUM to 4096

This isn't really ideal, but neither is hitting the limit due to maps with an excessive number of sprites that use clipshapes.

source/build/include/clip.h

@@ -16,7 +16,7 @@ extern "C" {
 #endif
 
 #define MAXCLIPSECTORS 512
-#define MAXCLIPNUM 2048
+#define MAXCLIPNUM 4096
 #define CLIPCURBHEIGHT (1<<8)
 #ifdef HAVE_CLIPSHAPE_FEATURE