Carla: Fix crash on plugins with latency but no activate/deactivate

c++/carla-backend/dssi.cpp

@@ -728,9 +728,13 @@ public:
                             ldescriptor->connect_port(handle, aOut.rindexes[j], tmpOut[j]);
                     }
 
-                    ldescriptor->activate(handle);
+                    if (ldescriptor->activate)
+                        ldescriptor->activate(handle);
+
                     ldescriptor->run(handle, 2);
-                    ldescriptor->deactivate(handle);
+
+                    if (ldescriptor->deactivate)
+                        ldescriptor->deactivate(handle);
 
                     m_latency = rint(paramBuffers[i]);
                     hasLatency = true;

c++/carla-backend/ladspa.cpp

@@ -697,9 +697,13 @@ public:
                             descriptor->connect_port(handle, aOut.rindexes[j], tmpOut[j]);
                     }
 
-                    descriptor->activate(handle);
+                    if (descriptor->activate)
+                        descriptor->activate(handle);
+
                     descriptor->run(handle, 2);
-                    descriptor->deactivate(handle);
+
+                    if (descriptor->deactivate)
+                        descriptor->deactivate(handle);
 
                     m_latency = rint(paramBuffers[i]);
                     hasLatency = true;

c++/carla-backend/lv2.cpp

@@ -1801,9 +1801,13 @@ public:
                             descriptor->connect_port(handle, aOut.rindexes[j], nullptr);
                     }
 
-                    descriptor->activate(handle);
+                    if (descriptor->activate)
+                        descriptor->activate(handle);
+
                     descriptor->run(handle, 0);
-                    descriptor->deactivate(handle);
+
+                    if (descriptor->deactivate)
+                        descriptor->deactivate(handle);
 
                     m_latency = rint(paramBuffers[i]);
                     hasLatency = true;