Cleanup: make WorktreeLoader.pathExists return what its name says

It returns true if the path is missing. It started out as
IsWorktreePathMissing, and was renamed without inverting its result
when it moved into the loader in de57cfd6ff.

Invert the result instead of renaming it back, so that the call site
reads `IsPathMissing: !self.pathExists(path)`. If we can't check the
path, it still counts as existing, as it always did.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

pkg/commands/git_commands/worktree_loader.go

@@ -53,7 +53,7 @@ func (self *WorktreeLoader) GetWorktrees() ([]*models.Worktree, error) {
 			path := strings.SplitN(splitLine, " ", 2)[1]
 
 			current = &models.Worktree{
-				IsPathMissing: self.pathExists(path),
+				IsPathMissing: !self.pathExists(path),
 				Path:          path,
 				// we defer populating GitDir until a loop below so that
 				// we can parallelize the calls to git rev-parse, and
@@ -158,12 +158,13 @@ func (self *WorktreeLoader) GetWorktrees() ([]*models.Worktree, error) {
 func (self *WorktreeLoader) pathExists(path string) bool {
 	if _, err := self.Fs.Stat(path); err != nil {
 		if errors.Is(err, iofs.ErrNotExist) {
-			return true
+			return false
 		}
+		// We can't tell, so we don't show the worktree as missing
 		self.Log.Errorf("failed to check if worktree path `%s` exists\n%v", path, err)
-		return false
+		return true
 	}
-	return false
+	return true
 }
 
 func (self *WorktreeLoader) rebasedBranch(worktree *models.Worktree) (string, bool) {