Type error from bad SVREF call escapes compiler

[Paul F. Dietz]

(defun bug008 (n)
  (let ((p (make-array n :initial-element nil)))
    (unless (svref p 0)
      (svref p nil))))

==>

The value
  NIL
is not of type
  REAL
   [Condition of type TYPE-ERROR]

Restarts:
 0: [ABORT] Exit debugger, returning to top level.

Backtrace:
  0: ((SB-C:DEFTRANSFORM SB-KERNEL:%CHECK-BOUND) #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME SB-KERNEL:%CHECK-BOUND :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHER..
  1: (SB-C::IR1-OPTIMIZE-COMBINATION #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME SB-KERNEL:%CHECK-BOUND :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHERE-FROM :DECL..
  2: (SB-C::IR1-OPTIMIZE #<SB-C:COMPONENT :NAME BUG008 :REANALYZE T {101EA2E363}> NIL)
  3: (SB-C::IR1-OPTIMIZE-UNTIL-DONE #<SB-C:COMPONENT :NAME BUG008 :REANALYZE T {101EA2E363}>)
  4: (SB-C::IR1-OPTIMIZE-PHASE-1 #<SB-C:COMPONENT :NAME BUG008 :REANALYZE T {101EA2E363}>)
  5: (SB-C::IR1-PHASES #<SB-C:COMPONENT :NAME BUG008 :REANALYZE T {101EA2E363}>)
  6: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME BUG008 :REANALYZE T {101EA2E363}>)
[...]