Fixed enum declaration values being parsed as int.

This caused values in the uint range to be made negative values.

Change-Id: Ia4284747f48508b589c034ff3aae0d141e96eb3c
Tested: on Linux.

src/idl_parser.cpp

@@ -1082,7 +1082,7 @@ CheckedError Parser::ParseEnum(bool is_union, EnumDef **dest) {
       }
       if (Is('=')) {
         NEXT();
-        ev.value = atoi(attribute_.c_str());
+        ev.value = StringToInt(attribute_.c_str());
         EXPECT(kTokenIntegerConstant);
         if (!opts.proto_mode && prevsize &&
             enum_def.vals.vec[prevsize - 1]->value >= ev.value)