Off-Importer: introduce unittest.

code/OFFLoader.cpp

@@ -294,7 +294,7 @@ void OFFImporter::InternReadFile( const std::string& pFile, aiScene* pScene, IOS
 
     // load faces with their indices
     faces = mesh->mFaces;
-    for (unsigned int i = 0; i < numFaces; ++i ) {
+    for (unsigned int i = 0; i < numFaces; ) {
         if(!GetNextLine(buffer,line)) {
             ASSIMP_LOG_ERROR("OFF: The number of faces in the header is incorrect");
             break;