HANDLER-BIND with empty bindings makes sneak through condition.

[CHIBA Masaomi]

(ignore-errors (handler-bind () (error "Foo")))
;error> Foo
;error> [Condition of type SIMPLE-ERROR]

SB-IMPL::%HANDLER-BIND can't manage the SB-KERNEL:*HANDLER-CLUSTERS* properly when binding is empty.
Apparently, regression from 1.2.5.

Expected:
(ignore-errors (handler-bind () (error "Foo")))
;=> NIL
; #<SIMPLE-ERROR "Foo" {100EFE15E3}>

SBCL Version: 1.2.5

uname -a
Linux t 3.16.5t #2 SMP Mon Oct 20 18:52:45 JST 2014 x86_64 GNU/Linux

*features*
(:ALIEN-CALLBACKS :ANSI-CL :ASH-RIGHT-VOPS :C-STACK-IS-CONTROL-STACK
 :COMMON-LISP :COMPARE-AND-SWAP-VOPS :COMPLEX-FLOAT-VOPS :CYCLE-COUNTER :ELF
 :FLOAT-EQL-VOPS :GENCGC :IEEE-FLOATING-POINT :INLINE-CONSTANTS :LARGEFILE
 :LINKAGE-TABLE :LINUX :LITTLE-ENDIAN :MEMORY-BARRIER-VOPS :MULTIPLY-HIGH-VOPS
 :OS-PROVIDES-BLKSIZE-T :OS-PROVIDES-DLADDR :OS-PROVIDES-DLOPEN
 :OS-PROVIDES-GETPROTOBY-R :OS-PROVIDES-POLL :OS-PROVIDES-PUTWC
 :OS-PROVIDES-SUSECONDS-T :PACKAGE-LOCAL-NICKNAMES :RAW-INSTANCE-INIT-VOPS
 :SB-AFTER-XC-CORE :SB-CORE-COMPRESSION :SB-DOC :SB-EVAL :SB-FUTEX :SB-LDB
 :SB-PACKAGE-LOCKS :SB-SIMD-PACK :SB-SOURCE-LOCATIONS :SB-TEST :SB-THREAD
 :SB-UNICODE :SB-XREF-FOR-INTERNALS :SBCL :STACK-ALLOCATABLE-CLOSURES
 :STACK-ALLOCATABLE-FIXED-OBJECTS :STACK-ALLOCATABLE-LISTS
 :STACK-ALLOCATABLE-VECTORS :STACK-GROWS-DOWNWARD-NOT-UPWARD :SYMBOL-INFO-VOPS
 :UNIX :UNWIND-TO-FRAME-AND-CALL-VOP :X86-64)