array-leader was NIL in REDISPLAY

[David Vinayak Wallace <Gumby@MIT-MC>]

In Symbolics 3600 Release 6.0, IP-TCP 29.0, AISite 9.4,
microcode TMC5-MIC 319, on Lisp Machine Jimi Hendrix:

The last line of my buffer was just a <page> by itself.  My curspor was
on it, I think.  If not, adjacent.  I typed c-X c-P and blooey!

>>Trap: The first argument given to the ARRAY-LEADER instruction, NIL, was not an array.
While in the function MOVE-BP  COM-MARK-PAGE  COMMAND-EXECUTE

MOVE-BP:  (P.C. = 53)
   Arg 0 (BP): ("" 1. :NORMAL)
   Arg 1 (LINE): NIL
   --Defaulted args:--
   Arg 2 (INDEX): NIL
   Local 3 (OLINE): ""

COM-MARK-PAGE:  (P.C. = 27)

COMMAND-EXECUTE:  (P.C. = 57)
   Arg 0 (COMMAND): COM-MARK-PAGE
   Arg 1 (CHAR): 336.
   Arg 2 (PREFIX-CHAR): 344.
   --Defaulted args:--
   Arg 3 (HOOK-LIST): NIL

MAKE-EXTENDED-COMMAND-INTERNAL:  (P.C. = 107)

Closure of MAKE-EXTENDED-COMMAND-INTERNAL:

COMMAND-EXECUTE:  (P.C. = 57)
   Arg 0 (COMMAND): #<DTP-CLOSURE 112451571>
   Arg 1 (CHAR): 344.
   Arg 2 (PREFIX-CHAR): NIL
   Arg 3 (HOOK-LIST): NIL

PROCESS-COMMAND-CHAR:  (P.C. = 14)
   Arg 0 (CH): 344.

(:METHOD EDITOR :EDIT):  (P.C. = 233)
   Arg 0 (SELF): #<ZMACS-TOP-LEVEL-EDITOR 121171573>
   Arg 1 (SELF-MAPPING-TABLE): #<Map to flavor EDITOR -- 12. IV's, 0. FL's 142346020>
   Arg 2 (OPERATION): :EDIT
   --Defaulted args:--
   Arg 3 (TOP-LEVEL-P): T
   Arg 4 (DESCRIPTION): NIL

(:METHOD TOP-LEVEL-EDITOR :COMBINED :EDIT):  (P.C. = 60)
   Arg 0 (SELF): #<ZMACS-TOP-LEVEL-EDITOR 121171573>
   Arg 1 (SELF-MAPPING-TABLE): #<Map to flavor TOP-LEVEL-EDITOR -- 13. IV's, 1. FL's 142345776>
   Arg 2 (.OPERATION.): :EDIT
   Rest arg (.DAEMON-CALLER-ARGS.): NIL

ZMACS-WINDOW-TOP-LEVEL:  (P.C. = 51)

SI:PROCESS-TOP-LEVEL:  (P.C. = 54)
   Arg 0 (IGNORE): NIL