fix Nightmare Gallery demo crash

src/prelaunch/nightmare.a

@@ -8,18 +8,25 @@
     !source "src/prelaunch/common.a"
 
          +ENABLE_ACCEL
+         +NEW_RESET_VECTOR $BE00
+
          lda   #$60
          sta   $404B
          jsr   $4000      ; decompress
 
-         lda   #<callback ; lets fix ROM calls to WAIT/$FCA8
+         ldx   #(callback_e-callback)-1
+-        lda   callback,x
+         sta   $BE20,x
+         dex
+         bpl   -
+         lda   #$20       ; lets fix ROM calls to WAIT/$FCA8
          sta   $16A9      ; which behave differently
          sta   $80EE      ; on different machines
          sta   $8799      ; (fixes slow scream on //c+ & //gs)
          sta   $8C8F
          sta   $8CC4
          sta   $8CE1
-         lda   #>callback
+         lda   #$BE
          sta   $16AA
          sta   $80EF
          sta   $879A
@@ -47,6 +54,7 @@ wait3    sbc   #$01
          sbc   #$01
          bne   wait2
          rts
+callback_e
 
 !if * > $1C0 {
   !error "code is too large, ends at ", *