SIBImporter: Add assertions to silence static analyzer warnings

code/SIBImporter.cpp

@@ -902,6 +902,7 @@ void SIBImporter::InternReadFile(const std::string& pFile,
     // Add nodes for each object.
     for (size_t n=0;n<sib.objs.size();n++)
     {
+        ai_assert(root->mChildren);
         SIBObject& obj = sib.objs[n];
         aiNode* node = new aiNode;
         root->mChildren[childIdx++] = node;
@@ -926,6 +927,7 @@ void SIBImporter::InternReadFile(const std::string& pFile,
     // (no transformation as the light is already in world space)
     for (size_t n=0;n<sib.lights.size();n++)
     {
+        ai_assert(root->mChildren);
         aiLight* light = sib.lights[n];
         if ( nullptr != light ) {
             aiNode* node = new aiNode;