fix(preview): Empty symbol preview

Fix simrat39/symbols-outline.nvim#176

I was going to pull @enddeadroyal's commit from their
'bugfix/symbol-hover-misplacement' branch in their fork but they changed
indentation so I had to apply the relevant changes myself instead.

However, credits for this fix goes to @enddeadroyal from the issue
commit in 176.

Also fixed the "No info available" markdown as it wasn't rendering
properly for me without a space after the '###'.

README.md

@@ -39,6 +39,7 @@ keep this list up to date.
 - Feat: when `auto_close=true` only auto close if `goto_location` is used (where
 focus changed), and not for `focus_location` (simrat39/symbols-outline.nvim#119)
 
+- Fix symbol preview (simrat39/symbols-outline.nvim#176)
 - Fix `SymbolsOutlineClose` crashing when already closed: simrat39/symbols-outline.nvim#163
 - Support Nerd fonts v3.0: simrat39/symbols-outline.nvim#225
 - Fix newlines in symbols crash: simrat39/symbols-outline.nvim#204 (simrat39/symbols-outline.nvim#184)

lua/symbols-outline/preview.lua

@@ -49,7 +49,7 @@ end
 
 local function get_hovered_node()
   local hovered_line = vim.api.nvim_win_get_cursor(so.view.winnr)[1]
-  local node = so.state.outline_items[hovered_line]
+  local node = so.state.flattened_outline_items[hovered_line]
   return node
 end
 
@@ -126,7 +126,7 @@ local function update_hover()
     end
     markdown_lines = vim.lsp.util.trim_empty_lines(markdown_lines)
     if vim.tbl_isempty(markdown_lines) then
-      markdown_lines = { '###No info available!' }
+      markdown_lines = { '### No info available!' }
     end
 
     markdown_lines = vim.lsp.util.stylize_markdown(