fix: prevent starting two finders when triggering GpChatFinder two times

[divramod]

hey hey again,

i don't know, if this is a minor one.

sometimes it happens, that i accedentially hit my map for opening the finder 2 times.
i then have the second finder window lying over the first one.
if i then exit the second one, the first one is still shown, but the cursor goes back to the buffer.
i have no way focussing the finder then, so i am stuck in the buffer and cannot see anything, because the finder lies over the buffer in which i am editing.
currently i need to restart vim for these cases.

it would be nice, if the plugin could ensure, that there will be only one finder window open max.

maybe even better, that it would toggle the finder, so the cursor is in the same position when opening it the next time.
that would be helpful for the task of renaming the topics from the past.