Figure.meca: Fix line and circle of offset parameter for dict/pandas input

[yvonnefroehlich]

Description of proposed changes

The line and the small circle are not plotted or modified via the offset parameter when passing a dictionary to the spec parameter of pygmt.Figure.meca.

Fixes / For context see: #2016 (comment)

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.

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