core: unify function behaviour of WTSVirtualChannelQuery

With all calls when WTSVirtualChannelQuery returns FALSE that means that
no ppBuffer was allocated, that was not the case with class=WTSVirtualChannelReady.
Most callers were not aware of that, leading to leaks for example when the channel is
not available client-side, the patch changes that so that you have to call call WTSFreeMemory
only if WTSVirtualChannelQuery returned TRUE.

libfreerdp/core/server.c

@@ -1693,9 +1693,9 @@ BOOL WINAPI FreeRDP_WTSVirtualChannelQuery(HANDLE hChannelHandle, WTS_VIRTUAL_CL
 						break;
 
 					default:
-						bval = FALSE;
-						status = FALSE;
-						break;
+						*ppBuffer = NULL;
+						*pBytesReturned = 0;
+						return FALSE;
 				}
 			}