swfmill segfaults on invalid input

[djcsdy]

Adrian Panasiuk reports (as bug #604104 on Launchpad):

The following xml reproducibly crashes swfmill xml2swf, version 0.3.0.

<?xml version="1.0" ?>
<swf>
        <Header framerate="25">
                <tags>
                        <DoInitAction>
                                <actions>
                                        <DeclareFunction2 argc="1"/>
                                </actions>
                        </DoInitAction>
                </tags>
        </Header>
</swf>

[djcsdy]

This fails because <DoInitAction> requires a sprite attribute. Unfortunately swfmill’s error reporting ranges from terrible to non-existent, so it crashes instead of informing you of the problem.