Better handling for plugins that set 0-size state

source/backend/engine/CarlaEngineBridge.cpp

@@ -877,7 +877,9 @@ public:
                         fShmNonRtServerControl.writeCustomData(cdata.key, keyLen);
 
                         fShmNonRtServerControl.writeUInt(valueLen);
-                        fShmNonRtServerControl.writeCustomData(cdata.value, valueLen);
+
+                        if (valueLen > 0)
+                            fShmNonRtServerControl.writeCustomData(cdata.value, valueLen);
 
                         fShmNonRtServerControl.commitWrite();
                         fShmNonRtServerControl.waitIfDataIsReachingLimit();

source/backend/plugin/CarlaPluginBridge.cpp

@@ -2115,7 +2115,9 @@ public:
                 const uint32_t valueSize(fShmNonRtServerControl.readUInt());
                 char value[valueSize+1];
                 carla_zeroChars(value, valueSize+1);
-                fShmNonRtServerControl.readCustomData(value, valueSize);
+
+                if (valueSize > 0)
+                    fShmNonRtServerControl.readCustomData(value, valueSize);
 
                 CarlaPlugin::setCustomData(type, key, value, false);
             }   break;