Allow parsers that don’t handle commands yet

Parsers serve two purposes:

1. They determine whether or not a command executes its arguments.
2. They determine which parts of a command’s arguments are other
   commands that get executed.

Before this change, parsers would have to do both, or else you would get
an AttributeError. Now, you can create a partial parser that can confirm
that a specific invocation doesn’t run any of its arguments but can’t
handle invocations that do run their arguments.

Specifically, this change is in preparation for adding a parser for
flatpak. flatpak has 43 built-in subcommands, some of which are able to
execute their arguments. I don’t want to bother adding a parser that
supports all 43 of those. I want to add a parser that supports a single
subcommand, and that subcommand can’t run its arguments.

resholve

@@ -3837,6 +3837,9 @@ class RecordCommandlike(object):
         return True
 
     def handle_external_generic(self, parsed, invocation):
+        if not hasattr(parsed, "commands"):
+            return True
+
         # TODO: shimming shells in here may be a bigger crime than
         #       duplicating the logic in two functions would be?
         shell = invocation.firstword in INVOKABLE_SHELLS