Environment

TOML++ version 3.2.0

Compiler:
GCC 10

C++ standard mode:
C++ 17

Library configuration overrides:
TOML_ENABLE_FORMATTERS 0
TOML_EXCEPTIONS 0

Describe the bug

Assert in unique_ptr::operator*

Steps to reproduce (or a small repro code sample)

Use value in TOML whih does not parse, like

[a]
b = [c"]

Additional information

• parser::parse_array() calls array::emplace_back() even if parse_value() fails
• array::emplace_back() does insert_at_back() and return *elems_.back(); - which is dereferencing nullptr.
• dereferencing nullptr is undefined behavior - MSVC lets it pass, but GCC (libstdcpp) has proper assert.

The simplest fix probably would be something like 4a4bf1e. I didn't do PR because I would expect that some of the tests running on GCC already found the problem.