Fix race with dwEventStatus

The problem is (in part) with the switch() that may read the variable
more than once.

==================
WARNING: ThreadSanitizer: data race (pid=10828)
  Write of size 8 at 0x7b040000ae78 by thread T6 (mutexes: write M0):
    #0 RFSetReaderEventState PCSC/src/readerfactory.c:1321:32 (pcscd+0x4c45ce)
    #1 EHStatusHandlerThread PCSC/src/eventhandler.c:382:11 (pcscd+0x4bee54)

  Previous read of size 8 at 0x7b040000ae78 by thread T8:
    #0 RFCheckReaderEventState PCSC/src/readerfactory.c:1350:24 (pcscd+0x4c46c6)
    #1 SCardStatus PCSC/src/winscard.c:1286:7 (pcscd+0x4ce7b5)
    #2 ContextThread PCSC/src/winscard_svc.c:635:16 (pcscd+0x4d0cc1)

  Location is heap block of size 16 at 0x7b040000ae70 allocated by thread T8:
    #0 malloc <null> (pcscd+0x42a65c)
    #1 RFAddReaderHandle PCSC/src/readerfactory.c:1249:14 (pcscd+0x4c43b4)
    #2 SCardConnect PCSC/src/winscard.c:491:7 (pcscd+0x4ccc16)
    #3 ContextThread PCSC/src/winscard_svc.c:502:16 (pcscd+0x4d0a70)

  Mutex M0 (0x7b4c000000a0) created at:
    #0 pthread_mutex_init <null> (pcscd+0x42d2fd)
    #1 RFAddReader PCSC/src/readerfactory.c:329:8 (pcscd+0x4c1d18)
    #2 HPAddDevice PCSC/src/hotplug_libudev.c:534:8 (pcscd+0x4cba1c)
    #3 HPEstablishUSBNotifications PCSC/src/hotplug_libudev.c:668:6 (pcscd+0x4cb4d4)

  Thread T6 (tid=11122, running) created by thread T2 at:
    #0 pthread_create <null> (pcscd+0x42be8b)
    #1 ThreadCreate PCSC/src/utils.c:184:8 (pcscd+0x4cc2dc)
    #2 EHSpawnEventHandler PCSC/src/eventhandler.c:237:7 (pcscd+0x4beb59)
    #3 RFAddReader PCSC/src/readerfactory.c:426:8 (pcscd+0x4c21b9)
    #4 HPAddDevice PCSC/src/hotplug_libudev.c:534:8 (pcscd+0x4cba1c)
    #5 HPEstablishUSBNotifications PCSC/src/hotplug_libudev.c:668:6 (pcscd+0x4cb4d4)

  Thread T8 (tid=11173, running) created by main thread at:
    #0 pthread_create <null> (pcscd+0x42be8b)
    #1 ThreadCreate PCSC/src/utils.c:184:8 (pcscd+0x4cc2dc)
    #2 CreateContextThread PCSC/src/winscard_svc.c:236:7 (pcscd+0x4cfd8b)
    #3 SVCServiceRunLoop PCSC/src/pcscdaemon.c:134:9 (pcscd+0x4c1082)
    #4 main PCSC/src/pcscdaemon.c:786:2 (pcscd+0x4c09c4)

SUMMARY: ThreadSanitizer: data race PCSC/src/readerfactory.c:1321:32 in RFSetReaderEventState
==================

src/readerfactory.c

@@ -1313,6 +1313,7 @@ LONG RFCheckReaderEventState(READER_CONTEXT * rContext, SCARDHANDLE hCard)
 {
  LONG rv;
  RDR_CLIHANDLES *currentHandle;
+ DWORD dwEventStatus;
 
  (void)pthread_mutex_lock(&rContext->handlesList_lock);
  currentHandle = list_seek(&rContext->handlesList, &hCard);
@@ -1324,7 +1325,8 @@ LONG RFCheckReaderEventState(READER_CONTEXT * rContext, SCARDHANDLE hCard)
  return SCARD_E_INVALID_HANDLE;
  }
 
- switch(currentHandle->dwEventStatus)
+ dwEventStatus = currentHandle->dwEventStatus;
+ switch(dwEventStatus)
  {
  case 0:
  rv = SCARD_S_SUCCESS;

src/readerfactory.h

@@ -98,7 +98,7 @@ THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  struct RdrCliHandles
  {
  SCARDHANDLE hCard; /**< hCard for this connection */
- DWORD dwEventStatus; /**< Recent event that must be sent */
+ _Atomic DWORD dwEventStatus; /**< Recent event that must be sent */
  };
 
  typedef struct RdrCliHandles RDR_CLIHANDLES;