mark: Make sure that jumplist item will not have zero lnum

Fixes #7169

test/functional/shada/marks_spec.lua

@@ -9,6 +9,8 @@ local shada_helpers = require('test.functional.shada.helpers')
 local reset, set_additional_cmd, clear =
   shada_helpers.reset, shada_helpers.set_additional_cmd,
   shada_helpers.clear
+local add_argv = shada_helpers.add_argv
+local nvim_argv = shada_helpers.nvim_argv
 
 local nvim_current_line = function()
   return curwinmeths.get_cursor()[1]
@@ -17,8 +19,10 @@ end
 describe('ShaDa support code', function()
   local testfilename = 'Xtestfile-functional-shada-marks'
   local testfilename_2 = 'Xtestfile-functional-shada-marks-2'
+  local non_existent_testfilename = testfilename .. '.nonexistent'
   before_each(function()
     reset()
+    os.remove(non_existent_testfilename)
     local fd = io.open(testfilename, 'w')
     fd:write('test\n')
     fd:write('test2\n')
@@ -214,4 +218,23 @@ describe('ShaDa support code', function()
     nvim_command('" sync 2')
     eq(2, nvim_current_line())
   end)
+
+  -- -c temporary sets lnum to zero to make `+/pat` work, so calling setpcmark()
+  -- during -c used to add item with zero lnum to jump list.
+  it('does not create incorrect file for non-existent buffers when writing from -c',
+  function()
+    add_argv('--cmd', 'silent edit ' .. non_existent_testfilename, '-c', 'qall')
+    local argv = nvim_argv(nil, '--headless')
+    eq('', funcs.system(argv))
+    eq(0, exc_exec('rshada'))
+  end)
+
+  it('does not create incorrect file for non-existent buffers opened from -c',
+  function()
+    add_argv('-c', 'silent edit ' .. non_existent_testfilename,
+             '-c', 'autocmd VimEnter * qall')
+    local argv = nvim_argv(nil, '--headless')
+    eq('', funcs.system(argv))
+    eq(0, exc_exec('rshada'))
+  end)
 end)