If set the number of history saves is 0, assertions fail when inserting an entry on exit.
Dont insert an entry when the number of saves is 0 fixes the issue.

fixes #11497

Problem:    Writing viminfo fails with a circular reference.
Solution:   Use copyID to detect the cycle. (closes vim/vim#6217)
https://github.com/vim/vim/commit/5b157fe2edfdce5f77080aeac2b4a03f39eb1c1a

Fix the problem of failing to write shada when the global variable contains
Funcref or Partial.

Since 8b8ecf4, the shada module loads files in the jumplist to properly
clear duplicates. This can trigger some autocommands, which in turn
saves and restores search and substitute patterns, freeing the previous
strings in "spats" which are held in "wms" as well (heap-use-after-free).
To avoid this, initialize the jumplist in "wms" before search patterns.

fixes #9775

Problems:
- In two places in shada_read_when_writing() memory just was not freed. Both 
  places were verified to cause test failures.
- Numbered marks got assigned incorrect (off-by-one compared to position in the 
  array) numbers in replace_numbered_mark.
- It was possible to have non-continuously populated array of numbered marks 
  which messed up code for merging them.

(Note about tests: marks with additional data are always compared different when 
merging, that caused some confusion regarding why test did not work the way 
I expected.)

Known to cause memory leak, but not an expected crash.