Only upload MQLS log entry with model results if there is no error

We currently have no way of differentiating between a successful run
with no results and a run that resulted in an error on the server.
Therefore this CL only emits the model run results if the model
execution was successful. This will allow us to stop setting
positive execution frequencies for sites for which the model has
determined that there are no relevant fields.

Bug: 372535824
Change-Id: I732c93d98e314463beaad027cf4be23b14d31509
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6587148
Reviewed-by: Florian Leimgruber <fleimgruber@google.com>
Commit-Queue: Jan Keitel <jkeitel@google.com>
Cr-Commit-Position: refs/heads/main@{#1465476}