🐛 fixing CBOR's indefinity length strings #961

Beside the fix discussed in #961, we also had to re-adjust a test case. It seems that it was failing before, and I "fixed" it to work with the broken implementation...

single_include/nlohmann/json.hpp

@@ -5768,8 +5768,7 @@ class binary_reader
                 string_t result;
                 while (get() != 0xFF)
                 {
-                    unexpect_eof();
-                    result.push_back(static_cast<char>(current));
+                    result.append(get_cbor_string());
                 }
                 return result;
             }