Boundary error in VCS_INFO_set --nvcs

[Bart Schaefer <schaefer@brasslantern.com>]

This output is from an older version of VCS_INFO but I don't see a
diff that would have changed anything but line numbers:

+vcs_info:52> VCS_INFO_set --nvcs
+VCS_INFO_set:5> setopt localoptions noksharrays NO_shwordsplit
+VCS_INFO_set:6> local -i i j
+VCS_INFO_set:8> [[ --nvcs == --nvcs ]]
+VCS_INFO_set:9> [[ '' == -preinit- ]]
+VCS_INFO_set:10> i=0
+VCS_INFO_set:11> typeset -gx 'vcs_info_msg_0_='
+VCS_INFO_set:10> i=-1
+VCS_INFO_set:11> typeset -gx 'vcs_info_msg_-1_='
VCS_INFO_set:typeset:11: not valid in this context: vcs_info_msg_-1_

The problem is that when disable-patterns matches the current
directory, vcs_info invokes VCS_INFO_set --nvcs, which hits this loop:

 if [[ $1 == '--nvcs' ]] ; then
     [[ $2 == '-preinit-' ]] && (( maxexports == 0 )) && (( maxexports = 1 ))
     for i in {0..$((maxexports - 1))} ; do

Because $2 is not "-preeinit-", when maxexports is zero it is never
reset to 1 and the "for" loop runs backwards to -1.  I don't otherwise
know how to reproduce the situation where VCS_INFO_maxexports is never
called.