Fixes: 659ecd0388 plugins: percol: Check for alias zz before unalias

The original patch (659ecd0388)
unaliases the percol alias, however, does not validate if the alias
is already defined. This leads to the following message that is shown
everytime a new bash session is spawned where this variable is not
defined when the percol plugin is enabled.

bash: unalias: zz: not found

plugins/available/percol.plugin.bash

@@ -35,7 +35,10 @@ if command -v percol>/dev/null; then
         bind -x '"\C-r": _replace_by_history'
 
         # bind zz to percol if fasd enable
+        if [[ $(type -t zz) == 'alias'  ]]; then
           unalias zz
+        fi
+
         if command -v fasd>/dev/null; then
             function zz() {
                 local l=$(fasd -d | awk '{print $2}' | percol)