Fix build failure: SubEditActivity Kotlin compile errors

[Copilot]

The CI build job failed at :app:compilePlaystoreDebugKotlin with three errors in SubEditActivity.kt: two unresolved toast references and a nullable/non-null type mismatch on the save path.

Changes

• Missing import: SubEditScreen calls context.toast(...) for validation errors, but only toastSuccess was imported. Added com.v2ray.ang.extension.toast.
• Nullable mismatch: buildSubItem() returns SubscriptionItem? (null after showing an error toast for an invalid override port or an Aether exit-chain selection), but its result was passed directly to the non-null onSave parameter. The save action now proceeds only on a non-null result:

val hasError = remarksErr || urlErr || intervalErr
if (!hasError) {
    buildSubItem()?.let { onSave(it) }
}

On the null path no save occurs, which matches the existing behavior since buildSubItem() has already surfaced the error toast.

[patterniha]

@copilot
? check more carefully
the original v2rayNG (2dust:master) code, use same code, but its build was done without error, so i don't think the error is because of your change

[Copilot]

@copilot
? check more carefully
the original v2rayNG (2dust:master) code, use same code, but its build was done without error, so i don't think the error is because of your change

I checked carefully — the failing code is not in upstream 2dust/v2rayNG. The upstream master version of SubEditActivity.kt differs from the PattNG copy in exactly the places that failed to compile:

1. Upstream buildSubItem() returns non-null SubscriptionItem and contains no toast calls — the LocalContext line is even commented out there. So upstream compiles fine.
2. The PattNG copy contains extra, PattNG-specific code that upstream does not have:
   • The subscription override-address/override-port UI and validation (overridePort state, R.string.toast_invalid_override_port) — these fields exist only in PattNG's SubscriptionItem (overrideAddress/overridePort, used in AngConfigManager.kt:452) and are not in upstream's DTO.
   • The Aether exit-chain guard: if (SettingsManager.getServerViaRemarks(nextProfile.trim())?.configType == EConfigType.AETHER) — the Aether config type is a PattNG-only feature.
   • To support those two features, PattNG's buildSubItem() was changed to return SubscriptionItem? and to call context.toast(...) — but the com.v2ray.ang.extension.toast import was never added, and the save call site still passed the now-nullable result directly to the non-null onSave parameter.

So the build failure was in the PattNG-specific feature code merged on top of upstream, not in upstream's shared code. The failing CI run (35714483160) also built a different tree (my-releases at f961533) than the current branch. My commit ee49c54 adds only the missing import and makes the save action proceed only when buildSubItem() returns non-null (the null path already shows the error toast), preserving the PattNG override-port and Aether behavior.