MAINT-7257 Added null check for volume manager

indra/llprimitive/llprimitive.cpp

@@ -172,7 +172,7 @@ LLPrimitive::~LLPrimitive()
 {
 	clearTextureList();
 	// Cleanup handled by volume manager
-	if (mVolumep)
+	if (mVolumep && sVolumeManager)
 	{
 		sVolumeManager->unrefVolume(mVolumep);
 	}