fix(Comms): check link connection state in _isSerialPortConnected

[ginolee218]

Description

On Android, LinkManager::_isSerialPortConnected() returned true as long as any
SerialLink instance was found in _rgLinks, without checking whether the link was
actually connected.

In `LinkManager::_addSerialAutoConnectLink()` on Android:
```cpp
if (AndroidSerial::usePosixSerial() || !_isSerialPortConnected()) {
    portList = QGCSerialPortInfo::availablePorts();
}

When a connected USB serial port disconnected, rebooted, or lost connection, the
disconnected SerialLink instance remained in _rgLinks. As a result,
_isSerialPortConnected() incorrectly continued to return true, blocking
QGCSerialPortInfo::availablePorts() from running. This caused auto-reconnect on Android
to stall after disconnection until the app was restarted.

This PR adds if (link->isConnected()) inside _isSerialPortConnected(), ensuring it only
reports true when a serial link is actively connected, allowing port scanning and auto-
reconnection to resume after a disconnect.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• CI/Build changes
• Other

Testing

• Tested locally
• Added/updated unit tests
• Tested with simulator (SITL)
• Tested with hardware

Platforms Tested

• Linux
• Windows
• macOS
• Android
• iOS

Flight Stacks Tested

• PX4
• ArduPilot

Screenshots

Checklist

• I have read the Contribution Guidelines
• I have read the Code of Conduct
• My code follows the project's coding standards
• I have added tests that prove my fix/feature works
• New and existing unit tests pass locally

Related Issues

---

By submitting this pull request, I confirm that my contribution is made under the terms of the project's dual license (Apache 2.0 and GPL v3).

[github-actions]

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A maintainer will review this soon. Please ensure:

• CI checks pass
• Code follows coding standards
• Changes tested on relevant platforms

We appreciate your contribution to QGroundControl!

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.49%. Comparing base (f29efd3) to head (c6460f3).
⚠️ Report is 354 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Comms/LinkManager.cc	0.00%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (30.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #15033      +/-   ##
==========================================
+ Coverage   25.47%   34.49%   +9.02%     
==========================================
  Files         769      945     +176     
  Lines       65912    85627   +19715     
  Branches    30495    39467    +8972     
==========================================
+ Hits        16788    29537   +12749     
+ Misses      37285    36459     -826     
- Partials    11839    19631    +7792     

Flag	Coverage Δ
unittests	34.49% <0.00%> (+9.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/Comms/LinkManager.cc	15.60% <0.00%> (+5.52%)	⬆️

... and 662 files with indirect coverage changes

---

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[github-actions]

Build Results

Platform Status

Platform	Status	Details
Linux	Passed	View
Windows	Passed	View
MacOS	Passed	View
Android	Passed	View

All builds passed.

Pre-commit

Check	Status	Details
pre-commit	Failed (non-blocking)	View

Pre-commit hooks: 2 passed, 76 failed, 7 skipped.

Test Results

linux-coverage-integration: 52 passed, 0 skipped
linux-coverage-unit: 185 passed, 0 skipped
linux-sanitizers-integration: 31 passed, 0 skipped
linux-sanitizers-unit: 185 passed, 0 skipped
Total: 453 passed, 0 skipped

Code Coverage

Coverage: 70.6%

No baseline available for comparison

Artifact Sizes

Artifact	Size
QGroundControl	253.10 MB
QGroundControl-aarch64	177.31 MB
QGroundControl-installer-AMD64	128.43 MB
QGroundControl-installer-AMD64-ARM64	70.81 MB
QGroundControl-installer-ARM64	99.56 MB
QGroundControl-linux	84.76 MB
QGroundControl-mac	84.76 MB
QGroundControl-x86_64	189.56 MB
No baseline available for comparison

---

_{Updated: 2026-09-03 10:17:38 UTC • Commit: c6460f3 • Triggered by: Linux}