Fix warnings for slow usage of length/1

Author: rrrene

lib/credo/check/readability/parentheses_on_zero_arity_defs.ex

@@ -47,7 +47,7 @@ defmodule Credo.Check.Readability.ParenthesesOnZeroArityDefs do
       {ast, ctx}
     end
 
-    defp walk({unquote(op), _, [{_, _, args} | _]} = ast, ctx) when length(args) > 0 do
+    defp walk({unquote(op), _, [{_, _, [_at_least_one_arg | _rest]} | _]} = ast, ctx) do
       {ast, ctx}
     end
 

lib/credo/check/refactor/variable_rebinding.ex

@@ -75,11 +75,7 @@ defmodule Credo.Check.Refactor.VariableRebinding do
         issue_for(ctx, variable_name, line)
       end)
 
-    if length(new_issues) > 0 do
-      {ast, put_issue(ctx, new_issues)}
-    else
-      {ast, ctx}
-    end
+    {ast, put_issue(ctx, new_issues)}
   end
 
   defp walk(ast, ctx) do