fix(display): reject trailing X11 display input

[unbridled-41]

Summary

Reject malformed X11 DISPLAY values containing trailing characters or extra numeric segments.

Root cause

std::stoi() was used without checking how many characters it consumed. Inputs such as localhost:0junk and localhost:0.1junk were therefore accepted because their numeric prefixes parsed successfully and the remaining characters were ignored.

Changes

• Check the consumed length for display and screen numbers.
• Reject unexpected text after the display number.
• Reject trailing characters and extra dot-separated segments after the screen number.
• Add regression tests for host and absolute Unix-socket forms.

Reproduction

Call getXOrgDisplay("localhost:0junk"). Before this change it returns a parsed display number of 0; after this change it returns an error.

Test plan

• Release build with the complete fix set
• Full CTest suite: 528 passed, 2 unrelated environment-dependent X11 tests skipped, 0 failed
• Added four focused malformed-input cases
• git diff --check

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: unbridled-41

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[deepin-ci-robot]

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