fuzzer failure --sub1.- interpreting as a short option

include/CLI/impl/App_inl.hpp

@@ -1974,7 +1974,8 @@ App::_parse_arg(std::vector<std::string> &args, detail::Classifier current_type,
                 }
                 std::string dummy1, dummy2;
                 bool val = false;
-                if(current_type == detail::Classifier::SHORT || detail::split_long(args.back(), dummy1, dummy2)) {
+                if((current_type == detail::Classifier::SHORT && detail::valid_first_char(args.back()[1])) ||
+                   detail::split_long(args.back(), dummy1, dummy2)) {
                     val = sub->_parse_arg(args, current_type, true);
                 }
 

tests/FuzzFailTest.cpp

@@ -341,7 +341,7 @@ TEST_CASE("app_roundtrip_parse_normal_fail") {
     // like HorribleErrors
     CLI::FuzzApp fuzzdata;
     auto app = fuzzdata.generateApp();
-    int index = GENERATE(range(1, 3));
+    int index = GENERATE(range(1, 4));
     std::string optionString, flagString;
     auto parseData = loadFailureFile("parse_fail_check", index);
     std::size_t pstring_start{0};