data_transfer: emit in main thread

Some clients can try to get the data info in the DataTransferEvent's callback
this can provide a deadlock on infoMutex_. To prevent that, emitting the signal
on the main thread is necessary.

Change-Id: Ifca032e497272c3da9e2a866a23e4883a142d1e9

src/data_transfer.cpp

@@ -127,7 +127,9 @@ DataTransfer::emit(DRing::DataTransferEventCode code) const
     }
     if (internalCompletionCb_)
         return; // VCard transfer is just for the daemon
+    runOnMainThread([id = id, code]() {
         emitSignal<DRing::DataTransferSignal::DataTransferEvent>(id, uint32_t(code));
+    });
 }
 
 //==============================================================================