fix Thexder launch

src/prelaunch/thexder.a

@@ -1,5 +1,5 @@
 ;license:MIT
-;(c) 2019 by qkumba/Frank M.
+;(c) 2019-2020 by qkumba/Frank M.
 
 !cpu 6502
 !to "build/PRELAUNCH/THEXDER",plain
@@ -9,15 +9,19 @@
 
          +ENABLE_ACCEL
          lda   #$60
+         sta   $83F
+         jsr   $800
+         lda   $13A8
+         cmp   #$4C
+         bne   +
+         lda   #$60
          sta   $13A8
          jsr   $1200
-
          +RESET_VECTOR reset
          lda   #<reset
          sta   $47FC
          lda   #>reset
          sta   $47FD      ; moved to LC $FFFC/D
-
          +DISABLE_ACCEL
          jmp   $1800
 
@@ -25,6 +29,9 @@ reset
          +READ_ROM_NO_WRITE
          jmp   $FAA6
 
++        +DISABLE_ACCEL
+         jmp   $1200
+
 !if * > $1C0 {
   !error "code is too large, ends at ", *
 }