Recursive needs processing

The current way needs relations are checked in void App::_process_requirements()
is missleading.
Assume you have an application 'test' with a CLI11 config system configuring
following needs relations between some subcommands:

app ---> sub1 ---> sub11
     |         |-> sub12
     |-> sub2

A) Current needs processing gives:
./test                  -> test requires sub1   // OK for the user
./test sub1             -> test requires sub2   // OK for the user
./test sub1 sub2        -> sub1 requires sub11  // Confuses the user
./test sub1 sub2 sub11  -> ready for execution

B) Recursive needs processing gives:
./test                  -> test requires sub1   // OK
./test sub1             -> sub1 requires sub11  // Much more intuitive for the user
./test sub1 sub2        -> sub1 requires sub11  // Makes sense: sub1 configuration is not compleate yet
./test sub1 sub11       -> test requires sub2   // OK, sub1 configuration is compleate
./test sub1 sub11 sub2  -> ready for execution

Author: VolkerChristian

include/CLI/impl/App_inl.hpp

@@ -1318,6 +1318,14 @@ CLI11_INLINE void App::_process_requirements() {
         }
     }
     for(const auto &subc : need_subcommands_) {
+        try {
+            subc->_process_requirements();
+        } catch (const CLI::RequiresError& e) {
+            if (subc->count() == 0) {
+                throw RequiresError(get_display_name(), subc->name_);
+            }
+            throw;
+        }
         if(subc->count_all() == 0) {
             missing_needed = true;
             missing_need = subc->get_display_name();
@@ -1402,7 +1410,7 @@ CLI11_INLINE void App::_process_requirements() {
                 }
             }
         }
-        if(sub->count() > 0 || sub->name_.empty()) {
+        if(sub->count() > 0 || sub->name_.empty() && !need_subcommands_.contains(sub.get())) {
             sub->_process_requirements();
         }