client/X11: Check arguments in xf_Bitmap_SetSurface

Arguments of xf_Bitmap_SetSurface are not checked before use currently
which may lead to segfaults. It may happen if bitmap is not found in a
cache from some reason. Let's check the arguments before use similarly
as it is done in client/Windows/wf_graphics.c in order to avoid segfaults.

https://github.com/FreeRDP/FreeRDP/issues/4117

client/X11/xf_graphics.c

@@ -202,6 +202,10 @@ static BOOL xf_Bitmap_SetSurface(rdpContext* context, rdpBitmap* bitmap,
                                  BOOL primary)
 {
 	xfContext* xfc = (xfContext*) context;
+
+	if (!context || (!bitmap && !primary))
+		return FALSE;
+
 	xf_lock_x11(xfc, FALSE);
 
 	if (primary)