[zsh] fix the manpath-caused errors on shell startup once and for all

zsh/path.zsh

@@ -12,7 +12,7 @@ path_prepend() {
   fi
   local var_name="$1"; shift
   local value; for value in "$@"; do
-    if eval "(( \${${var_name}[(ie)\$value]} > \${#${var_name}} ))"; then
+    if eval "(( \${${var_name}[(ie)\$value]-1} > \${#${var_name}} ))"; then
       eval "${var_name}=(\"\$value\" \"\${${var_name}[@]}\")"
     fi
   done

zsh/zplg.zsh

@@ -399,7 +399,7 @@ plugin() {
       else
         value="${plugin_dir}/${value}"
       fi
-      if eval "(( \${${var_name}[(ie)\$value]} > \${#${var_name}} ))"; then
+      if eval "(( \${${var_name}[(ie)\$value]-1} > \${#${var_name}} ))"; then
         case "$operator" in
           prepend) eval "$var_name=(\"\$value\" \${$var_name[@]})" ;;
            append) eval "$var_name=(\${$var_name[@]} \"\$value\")" ;;

zsh/zshrc

@@ -46,15 +46,20 @@ _perf_timer_start "total"
   fi
 # }}}
 
+# For some reason manpath is not always set when logging with ssh for instance.
+# Let's ensure that it is always set and exported. The additional colon ensures
+# that the system manpath isn't overwritten (see manpath(1)), though in reality
+# two colons get added for some reason, which is also valid, but means
+# something slightly different (again, see manpath(1)). Hope this won't cause
+# any problems in the future.
+export MANPATH="$MANPATH:"
+
 for script in functions options path env plugins aliases completion zle prompt colorscheme; do
   _perf_timer_start "$script.zsh"
   source "$ZSH_DOTFILES/$script.zsh"
   _perf_timer_stop "$script.zsh"
 done
 
-# add colon after MANPATH so that it doesn't overwrite system MANPATH
-MANPATH="$MANPATH:"
-
 command_exists rbenv && eval "$(rbenv init -)"
 
 _perf_timer_stop "total"