Fix out-of-bounds read in error code format parsing

[IfkumRfnl]

Summary

The std::error_code formatter read past the end of a format string when the string ended after an alignment specifier, for example, "{:>".

Added a check after alignment parsing to prevent this read:

if (it == end) return it;

Removed the redundant check before width parsing. Added two regression tests. Both tests failed with AddressSanitizer before the fix. All 28 std-test tests pass with AddressSanitizer after the fix.

[vitaut]

Thanks for the fix. Overall looks good but one regression test should be sufficient, let's remove the redundant error_code_truncated_fill_alignment test.

[IfkumRfnl]

Thanks for looking into it, removed the test.