Don't call SP::SPTextureManager::get() if not GLSL to avoid leaking

src/graphics/material_manager.cpp

@@ -23,6 +23,7 @@
 #include <sstream>
 
 #include "config/user_config.hpp"
+#include "graphics/central_settings.hpp"
 #include "graphics/material.hpp"
 #include "graphics/particle_kind_manager.hpp"
 #include "graphics/sp/sp_texture_manager.hpp"
@@ -57,9 +58,10 @@ MaterialManager::MaterialManager()
 MaterialManager::~MaterialManager()
 {
 #ifndef SERVER_ONLY
-    SP::SPTextureManager::get()->stopThreads();
+    if (CVS->isGLSL())
+        SP::SPTextureManager::get()->stopThreads();
 #endif
-    
+
     for(unsigned int i=0; i<m_materials.size(); i++)
     {
         delete m_materials[i];