asan: isolate variable use code

It looks like ASAN errors are not related to the new autocmd but to the
bdelete ex cmd that seems to break related to the deleted buffer.

test/functional/autocmd/autocmd_spec.lua

@@ -98,10 +98,27 @@ describe('autocmds:', function()
     local second_buffer = eval("bufnr('%')")
     command('autocmd WinClosed <buffer> :let g:triggered+=1 | bdelete ' .. second_buffer)
     command('tabnew')
-    command('bdelete ' .. second_buffer )
+    command('bdelete ' .. second_buffer)
     eq(1, eval('g:triggered'))
   end)
 
+  it('bdelete doesnt break existing variables', function()
+    command('let g:variable = 0')
+    local first_buffer = eval("bufnr('%')")
+    command('new')
+    local second_buffer = eval("bufnr('%')")
+    command('tabnew')
+    command('bdelete ' .. second_buffer)
+    eq(0, eval('g:variable'))
+  end)
+
+  it('bdelete doesnt break bufwinnr', function()
+    command('new')
+    local second_buffer = eval("bufnr('%')")
+    command('bdelete ' .. second_buffer )
+    eq(-1, funcs.bufwinnr(second_buffer))
+  end)
+
   it('v:vim_did_enter is 1 after VimEnter', function()
     eq(1, eval('v:vim_did_enter'))
   end)