bug in 'b' array parameter subscript flag

[Greg Klanderman <gak@xxxxxxxxxxxxxx>]

when the 'b' flag is used with the 'i' flag, and there are no elements
to be searched, '0' is incorrectly returned rather than one plus the
array length:

[~] phl| zsh -f
phl% echo $ZSH_VERSION 
4.3.10-dev-1
phl% echo $ZSH_PATCHLEVEL 
1.4718
phl% unsetopt ksharrays
phl% a=(bar) 
phl% echo $#a
1
phl% echo ${a[(ib:2:)foo]}    ## BUG: this should return 2
0
phl% echo ${a[(i)foo]}        ## just like this
2

the 'b' flag works correctly when the number of elements to be
searched is non-zero:

phl% a=(bar baz)
phl% echo $#a             
2
phl% echo ${a[(ib:2:)foo]}
3

also, the 'i' flag alone, with no elements to search works correctly:

phl% a=()
phl% echo $#a             
0
phl% echo ${a[(i)foo]}    
1


cheers,
greg