[audioplugins] give AudioPluginState::Undefined an explicit wire name

audioPluginStateName(Undefined) returned "" — indistinguishable from an
unknown name. Add an explicit Undefined<->"Undefined" entry so the
mapping is bijective. writePluginsInfo still omits the state field for
Undefined entries, so the JSON wire format is unchanged.

Author: luapmartin

framework/audioplugins/audiopluginstypes.h

@@ -131,6 +131,7 @@ namespace detail {
 inline const std::map<AudioPluginState, std::string>& audioPluginStateNames()
 {
     static const std::map<AudioPluginState, std::string> NAMES = {
+        { AudioPluginState::Undefined, "Undefined" },
         { AudioPluginState::Discovered, "Discovered" },
         { AudioPluginState::Validated, "Validated" },
         { AudioPluginState::Missing, "Missing" },

framework/audioplugins/internal/knownaudiopluginsregister.cpp

@@ -351,8 +351,9 @@ Ret KnownAudioPluginsRegister::writePluginsInfo()
         obj.set("meta", metaToJson(info.meta, runtimeOnly));
         obj.set("path", info.path.toStdString());
 
-        // Skip writing the state field for Undefined (would serialize as "");
-        // load() reads a missing/empty "state" as Undefined too, so this round-trips.
+        // Omit the state field for Undefined entries — a written entry always
+        // carries a concrete state. load() reads a missing "state" back as
+        // Undefined, so this round-trips.
         if (info.state != AudioPluginState::Undefined) {
             obj.set("state", audioPluginStateName(info.state));
         }