Fix bug #62900: Wrong namespace on xsd import error message

The one error message indeed had a wrong namespace, and in general they
weren't very descriptive, this also makes them more de

Fix bug #62900: Wrong namespace on xsd import error message

The one error message indeed had a wrong namespace, and in general they
weren't very descriptive, this also makes them more descriptive.

Furthermore, two additional bugs were fixed:
- Persistent memory leak of `location`.
- UAF issues when printing the error message.

Closes GH-15830.

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