refactor: Refactored RequestMethodString function to follow developer notes

Removed the default case in the switch statement in order to comply with the Developer Notes

src/httpserver.cpp

@@ -198,9 +198,10 @@ std::string RequestMethodString(HTTPRequest::RequestMethod m)
         return "HEAD";
     case HTTPRequest::PUT:
         return "PUT";
-    default:
+    case HTTPRequest::UNKNOWN:
         return "unknown";
-    }
+    } // no default case, so the compiler can warn about missing cases
+    assert(false);
 }
 
 /** HTTP request callback */