Fixing a logical error causing a panic in some very rare cases

Dependencies

• [2] L5CVF6UJ Debugging
• [3] QEUTVAZ4 Splitting btree::page
• [4] T73WR2BX Cleaner RC increments for keys and values containing references + more comments in `del`
• [*] OP6SVMOD Resetting history

Change contents

• replacement in sanakirja-core/src/btree/del.rs at line 502
  [3.5671]→[2.6579:6613](∅→∅)
  − if !mod_is_left {
  [3.5671]

  [2.6613]
  +

  + // If this split isn't at the root, and the page

  + // modified in the last step is the one on the left of

  + // the entry, move back one step before inserting the

  + // split key/value.

  + //

  + // (remember that we popped the stack upon entering

  + // this function).

  + if cursor.len() > 0 && !mod_is_left {