Don't generate MIN & MAX enum values if "--no-prefix" is used.

Close #3892

src/idl_gen_cpp.cpp

@@ -179,6 +179,7 @@ static void GenEnum(const Parser &parser, EnumDef &enum_def,
     maxv = !maxv || maxv->value < ev.value ? &ev : maxv;
     anyv |= ev.value;
   }
+  if (parser.opts.scoped_enums || parser.opts.prefixed_enums) {
     assert(minv && maxv);
     if (enum_def.attributes.Lookup("bit_flags")) {
       if (minv->value != 0) // If the user didn't defined NONE value
@@ -191,6 +192,7 @@ static void GenEnum(const Parser &parser, EnumDef &enum_def,
       code += "  " + GenEnumVal(enum_def, "MAX", parser.opts) + " = ";
       code += GenEnumVal(enum_def, maxv->name, parser.opts) + "\n";
     }
+  }
   code += "};\n";
   if (parser.opts.scoped_enums && enum_def.attributes.Lookup("bit_flags"))
     code += "DEFINE_BITMASK_OPERATORS(" + enum_def.name + ", " +  GenTypeBasic(enum_def.underlying_type, false) + ")\n";