cli: fix render command without extra arguments

rendercv/cli.py

@@ -586,6 +586,7 @@ def cli_command_render(
         # double dashed, such as `--cv.sections.education.0.institution`. The following
         # elements are the corresponding values of the key, such as
         # `"Bogazici University"`. The for loop below parses `ctx.args` accordingly.
+        if ctx:
             for i in range(0, len(ctx.args), 2):
                 key = ctx.args[i]
                 value = ctx.args[i + 1]