CCBC-1187: lcb_respexists_is_found returns true for deleted documents.

We could either add a lcb_respexists_is_deleted api, or just have
is_found return false if the doc's deleted flag is set.  I chose
the latter.

Change-Id: I9feb5e86257f4f953fb0665c22df498ff05f3054
Reviewed-on: http://review.couchbase.org/c/libcouchbase/+/127443
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Build Bot <build@couchbase.com>

src/operations/exists.cc

@@ -26,7 +26,7 @@ LIBCOUCHBASE_API lcb_STATUS lcb_respexists_status(const lcb_RESPEXISTS *resp)
 
 LIBCOUCHBASE_API int lcb_respexists_is_found(const lcb_RESPEXISTS *resp)
 {
-    return resp->ctx.rc == LCB_SUCCESS;
+    return resp->ctx.rc == LCB_SUCCESS && !resp->deleted;
 }
 
 LIBCOUCHBASE_API lcb_STATUS lcb_respexists_error_context(const lcb_RESPEXISTS *resp,