fix(client): unblock sync when teamserver has no data to send

[ROCKLEE-1998]

Summary

When the teamserver has no packets to synchronize, it still sends SYNC_START (count=0) followed by SYNC_FINISH. The client's count <= 0 branch in ProcessSyncPacket.cpp set sync = false and returned, which made the subsequent SYNC_FINISH handler a no-op (it early-returns when !sync). As a result finalizeSyncIfReady() never ran, so the splash screen was never closed and SyncedSignal was never emitted, leaving the client stuck on "data synchronization".

This change keeps sync = true in the count <= 0 branch so the incoming SYNC_FINISH properly finalizes the (empty) sync: it closes the splash screen and emits SyncedSignal.

Changes

• AdaptixClient/Source/Client/ProcessSyncPacket.cpp: in the count <= 0 branch, keep sync = true, reset the batch counters, call setSyncUpdateUI(false), and initialize the dialog with count so the upcoming SYNC_FINISH can finalize.

Test plan

• Client builds cleanly (incremental CMake build, only pre-existing Qt deprecation warnings).
• Connect a client to a teamserver that has no stored packets and confirm the splash closes and the UI becomes usable (no longer stuck on "data synchronization").
• Confirm the normal (count > 0) sync path is unaffected.