fix(#3134): setting one glyph to "" no longer disables others (#3136)

fix: fixes #3134

lua/nvim-tree/renderer/decorator/init.lua

@@ -112,9 +112,8 @@ function Decorator:define_sign(icon)
       vim.fn.sign_undefine(name)
     end
 
-    -- don't use sign if not defined
+    -- don't render sign if empty
     if #icon.str < 1 then
-      self.icon_placement = "none"
       return
     end