The add subcommand function was not exception safe. It added the subc…

…ommand to the vector before checking the already added option. This would result in duplicate subcommands being in place in the subcommands_ vector. The modifications make it exception safe and remove what I think was an unnecessary check for pointer duplication, that as far as I can tell was always false since it was comparing a newly created pointer directly to previously created ones.

include/CLI/App.hpp

@@ -1080,11 +1080,11 @@ class App {
 
     /// Add a subcommand. Inherits INHERITABLE and OptionDefaults, and help flag
     App *add_subcommand(std::string subcommand_name, std::string description = "") {
-        subcommands_.emplace_back(new App(description, subcommand_name, this));
+        CLI::App_p subcom(new App(description, subcommand_name, this));
         for(const auto &subc : subcommands_)
-            if(subc.get() != subcommands_.back().get())
-                if(subc->check_name(subcommands_.back()->name_) || subcommands_.back()->check_name(subc->name_))
-                    throw OptionAlreadyAdded(subc->name_);
+            if(subc->check_name(subcommand_name) || subcom->check_name(subc->name_))
+                throw OptionAlreadyAdded(subc->name_);
+        subcommands_.push_back(std::move(subcom));
         return subcommands_.back().get();
     }