cabana: fixed the issue of parsing multiplexed signals (#28660)

tools/cabana/dbc/dbc.cc

@@ -111,6 +111,9 @@ void cabana::Msg::update() {
   for (auto sig : sigs) {
     sig->multiplexor = sig->type == cabana::Signal::Type::Multiplexed ? multiplexor : nullptr;
     if (!sig->multiplexor) {
+      if (sig->type == cabana::Signal::Type::Multiplexed) {
+        sig->type = cabana::Signal::Type::Normal;
+      }
       sig->multiplex_value = 0;
     }
   }

tools/cabana/dbc/dbcfile.cc

@@ -136,7 +136,6 @@ void DBCFile::parse(const QString &content) {
           dbc_assert(++multiplexor_cnt < 2, "Multiple multiplexor");
           s.type = cabana::Signal::Type::Multiplexor;
         } else {
-          dbc_assert(multiplexor_cnt == 1, "No multiplexor");
           s.type = cabana::Signal::Type::Multiplexed;
           s.multiplex_value = indicator.mid(1).toInt();
         }