ODBC Unicode wrappers do not check for null length pointers

[aleks-f]

Describe the bug
Unicode wrappers indiscriminately use length pointer, even when caller sends null:

poco/Data/ODBC/src/Unicode_WIN32.cpp

Line 52 in 03c2fa3

makeUTF8(buffer, *pcbCharAttr, pCharAttr, cbCharAttrMax);

poco/Data/ODBC/src/ConnectionHandle.cpp

Lines 267 to 271 in 03c2fa3

	if (Utility::isError(Poco::Data::ODBC::SQLGetConnectAttr(_hdbc,
	SQL_ATTR_CONNECTION_DEAD,
	&value,
	sizeof(value),
	0))) return false;

Relevant environment information:

• OS: Any
• Poco version: All
• ODBC

Caller may not be interested in such details, so passing null should be permitted and dealt with internally in the function