fix(amazonq): skip edit suggestion if applyDiff fail

[Will-ShaoHua]

Problem

applyDiff may fail and the consequence is the newCode to update become empty string, thus deleting all users' code.

Before

Screen.Recording.2025-07-17.at.1.11.54.AM.mov

After

Screen.Recording.2025-07-17.at.10.06.45.AM.mov

Solution

---

• Treat all work as PUBLIC. Private feature/x branches will not be squash-merged at release time.
• Your code changes must meet the guidelines in CONTRIBUTING.md.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
  • Confirm whether tests should be added or ensure the PR description explains why tests are not required.
• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
  • Note: beta or "experiment" features that have active users should announce fixes in the changelog.
  • If this is not a feature or fix, use an appropriate type from the title guidelines. For example, telemetry-only changes should use the telemetry type.