[v5] Fix unintended zero set in Sparc printInst

[david942j]

Your checklist for this pull request

• [x] I've documented or updated the documentation of every API function and struct this PR changes.
• [x] I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

The null byte should be set after the mnemonic string instead of overwriting the last byte of it.

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Test plan

Updated suite/cs_test/issues.cs with a Sparc jump with condition instruction and confirmed ./build/cstest -f ./issues.cs failed without the fix.

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Closing issues

Fixes #2419

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