Fix an issue with command listeners not retaining the help/info messages. Credits @DrakezZ for spotting the issue.

source/Command.hpp

@@ -1290,11 +1290,11 @@ public:
         // Assign the specifier, if any
         if (spec)
         {
-            m_Spec.clear();
+            m_Spec.assign(spec);
         }
         else
         {
-            m_Spec.assign(spec);
+            m_Spec.clear();
         }
     }