QDBusArgument MapType fits all kinds of maps but when we try to stream a map of type other than a{sv} (which the MRPIS spec requires) into a QVariantMap we would crash. Explicitly check signature to avoid this.

BUG: 374531
FIXED-IN: 5.8.6

This is clearly an application bug, Metadata *must* be a{sv} according to spec but we shouldn't render Plasma unusable if a client is stupid.

Verified that metadata in VLC player (album art, artist, etc) still works

I'll try to create a small testcase and report that issue to Qt, it shouldn't crash in

QVariantMap map;
map << arg; // oops, it's not a{sv} but a{ss}