fix(priority): don't insert empty [# ] cookie when clearing priority

Headline:set_priority only treated a blank priority as "remove the
cookie" when a cookie already existed. The other two branches ran when
the headline had no cookie yet. They always built a new cookie, even
when the priority was blank.

As a result, pressing <Space> at the priority prompt on a headline
without an existing cookie returned " " from PriorityState:prompt_user,
which fell through to an insertion branch and produced a literal
[# ] cookie instead of clearing the priority.

Bring the empty check to the top of set_priority so it applies to all
paths: if the trimmed priority is empty, remove the existing cookie if
present, otherwise do nothing. The insertion branches now only run with
a real priority and can no longer fabricate an empty cookie.

Author: liamrlawrence

lua/orgmode/files/headline.lua

@@ -347,9 +347,15 @@ end
 ---@param priority string
 function Headline:set_priority(priority)
   local _, priority_node = self:get_priority()
+  if vim.trim(priority) == '' then
+    if priority_node then
+      return self:_set_node_text(priority_node, '')
+    end
+    return
+  end
+
   if priority_node then
-    local text = (vim.trim(priority) == '') and '' or ('[#%s]'):format(priority)
-    return self:_set_node_text(priority_node, text)
+    return self:_set_node_text(priority_node, ('[#%s]'):format(priority))
   end
 
   local todo, todo_node = self:get_todo()

tests/plenary/ui/mappings/priority_spec.lua

@@ -62,6 +62,17 @@ describe('Priority mappings', function()
     assert.are.same('* TODO Test orgmode', vim.fn.getline(1))
   end)
 
+  it('should do nothing if <Space> is pressed on a line without a priority', function()
+    alpha_config()
+    helpers.create_file({
+      '* TODO Test orgmode',
+    })
+    vim.fn.cursor(1, 1)
+    assert.are.same('* TODO Test orgmode', vim.fn.getline(1))
+    vim.cmd('norm ,o, \r')
+    assert.are.same('* TODO Test orgmode', vim.fn.getline(1))
+  end)
+
   it('should add a priority if the item does not already have one', function()
     helpers.create_file({
       '* TODO Test orgmode',