Remove a wrong call to git_mwindow_close which caused a segfault if it
ever did run. In that same piece of code, if the LRU was from the
first wiindow in the list in a different file, we didn't update that
list, so the first element had been freed.

Fix these two issues.

Signed-off-by: Carlos Martín Nieto <carlos@cmartin.tk>