Fixes Heap-buffer-overflow READ 4 in Assimp::ScenePreprocessor::ProcessMesh

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=49797

code/AssetLib/OFF/OFFLoader.cpp

@@ -292,6 +292,7 @@ void OFFImporter::InternReadFile( const std::string& pFile, aiScene* pScene, IOS
         if(!idx || idx > 9) {
 	        ASSIMP_LOG_ERROR("OFF: Faces with zero indices aren't allowed");
             --mesh->mNumFaces;
+            ++i;
             continue;
 	    }
 	    faces->mNumIndices = idx;