`toggle_dotfile` cause memory corruption

[kalocsaibotond]

I played around with Sfm-s toggle dotfile and I found a case where memory corruption occur.
I tested it on Void Linux.
Steps to reproduce:

1. Open Sfm in the home directory
2. Press G to jump to the last entry.
3. Press . to toggle dotfiles

Result:

(The homedir has way more dotfiles then not dotfiles)

I believe it is related to another segmentation fault error. Sometimes when I select large number of entries (100 - 200) with move_cursor in visual mode, then use cd_to_parent, I get segmentation fault.:

In addition, when I tried to write a patch for cd_to_parent to put the cursor on the parent, and center the view to it, when current_pane->start_index was anything other than zero, I got memory corruption for smaller non-zero values and I got segmentation fault at larger values (~50 or above).