Load workspace should activate the graph by default. (#7389)

Signed-off-by: rhhong <rhhong@amazon.com>

Gems/EMotionFX/Code/EMotionFX/Tools/EMotionStudio/EMStudioSDK/Source/Workspace.cpp

@@ -344,8 +344,9 @@ namespace EMStudio
             if (itActivationIndices->second.m_animGraphCommandIndex != -1
                 && itActivationIndices->second.m_motionSetCommandIndex != -1)
             {
-                commandString = AZStd::string::format("ActivateAnimGraph -actorInstanceID %%LASTRESULT%d%% -animGraphID %%LASTRESULT%d%% -motionSetID %%LASTRESULT%d%% -visualizeScale %f\n",
-                        (commandIndex - itActivationIndices->second.m_actorInstanceCommandIndex),
+                // Since the actor instance will be created by the component, we pass in -1 as the actor instance id so the activate anim graph command
+                // will pick up the first available actor instance.
+                commandString = AZStd::string::format("ActivateAnimGraph -actorInstanceID -1 -animGraphID %%LASTRESULT%d%% -motionSetID %%LASTRESULT%d%% -visualizeScale %f\n",
                         (commandIndex - itActivationIndices->second.m_animGraphCommandIndex),
                         (commandIndex - itActivationIndices->second.m_motionSetCommandIndex),
                         animGraphInstance->GetVisualizeScale());