Fix assigning not null-terminated string.

[likema]

The result buffer of ACE_TEXT_RegQueryValueEx may not be null-terminated.

This bug can be also reproduced on 6.5.x branch.

[jwillemsen]

Please extend one of the unit tests under ACE/tests with a reproducer

[likema]

Please extend one of the unit tests under ACE/tests with a reproducer

It may not be do it easily.

https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regqueryvalueexa#remarks shows

If the data has the REG_SZ, REG_MULTI_SZ or REG_EXPAND_SZ type, the string may not have been stored with the proper terminating null characters. Therefore, even if the function returns ERROR_SUCCESS, the application should ensure that the string is properly terminated before using it; otherwise, it may overwrite a buffer. (Note that REG_MULTI_SZ strings should have two terminating null characters.) One way an application can en`sure that the string is properly terminated is to use RegGetValue, which adds terminating null characters if needed.