change texture renaming logic to increase performance

ResourceGroupManager::resourceExistsInAnyGroup is slow (at least on
windows) if the tested path does not exist, but is fast if it does (due
to finding it in the index). This change tries the '.dds' version of the
name first, and reverts to the original if the '.dds' version was not
found.

components/nifogre/ogre_nif_loader.cpp

@@ -536,11 +536,23 @@ static Ogre::String getMaterial(const NiTriShape *shape, const Ogre::String &nam
              * textures from tga to dds for increased load speed, but all
              * texture file name references were kept as .tga.
              */
-            texName = "textures\\" + st->filename;
-            if(!Ogre::ResourceGroupManager::getSingleton().resourceExistsInAnyGroup(texName))
+
+            static const char * path = "textures\\";
+
+            texName = path + st->filename;
+            
+            Ogre::String::size_type pos = texName.rfind('.');
+
+            if (texName.compare (pos, texName.size () - pos, ".dds") != 0)
             {
-                Ogre::String::size_type pos = texName.rfind('.');
+                // since we know all (GOTY edition or less) textures end
+                // in .dds, we change the extension
                 texName.replace(pos, texName.length(), ".dds");
+
+                // if it turns out that the above wasn't true in all cases (not for vanilla, but maybe mods)
+                // verify, and revert if false (this call succeeds quickly, but fails slowly)
+                if(!Ogre::ResourceGroupManager::getSingleton().resourceExistsInAnyGroup(texName))
+                    texName = path + st->filename;
             }
         }
         else warn("Found internal texture, ignoring.");