Ensure generic IWXXM message parsing is always able to return a result whenever the model object is buildable.

[patrick-alaspaa]

• Parsing must obey ConversionHints.KEY_PARSING_MODE value.
• Any value required in IWXXM message is required in ConversionHints.VALUE_PARSING_MODE_STRICT mode.
• Mode ConversionHints.VALUE_PARSING_MODE_ALLOW_ANY_ERRORS should return a value always when the message is readable (as string).

This is to ensure that as much as possible data can be processed, and errors / missing data can be logged as exact as possible.

[patrick-alaspaa]

Though the parsing mode is never directly taken into consideration the conditions for this issue are met implicitly due to schematron checks and the way the the messages are parsed