output/pulse: fix crash during auto-detection

The PulseOutput needs to be "enabled" before WaitConnection() may be
called.

Closes #207

src/output/plugins/PulseOutputPlugin.cxx

@@ -27,6 +27,7 @@
 #include "../Wrapper.hxx"
 #include "mixer/MixerList.hxx"
 #include "mixer/plugins/PulseMixerPlugin.hxx"
+#include "util/ScopeExit.hxx"
 #include "Log.hxx"
 
 #include <pulse/thread-mainloop.h>
@@ -854,7 +855,10 @@ PulseOutput::TestDefaultDevice()
 try {
 	const ConfigBlock empty;
 	PulseOutput po(empty);
+	po.Enable();
+	AtScopeExit(&po) { po.Disable(); };
 	po.WaitConnection();
+
 	return true;
 } catch (const std::runtime_error &e) {
 	return false;