ceph-backport.sh: fix bugs in data_binary generation

The recently added code for generating the JSON for updating the PR milestone
and labels, via the --data-binary option of curl, was buggy.

Signed-off-by: Nathan Cutler <ncutler@suse.com>

src/script/ceph-backport.sh

@@ -813,7 +813,7 @@ function maybe_update_pr_milestone_labels {
     needs_milestone="$(backport_pr_needs_milestone)"
     if [ "$needs_milestone" ] ; then
         debug "Attempting to set ${milestone} milestone in ${backport_pr_url}"
-        data_binary="${data_binary}\"milestone\":\"${milestone_number}\""
+        data_binary="${data_binary}\"milestone\":${milestone_number}"
     else
         info "Backport PR ${backport_pr_url} already has ${milestone} milestone"
     fi
@@ -824,7 +824,9 @@ function maybe_update_pr_milestone_labels {
         fi
         data_binary="${data_binary}\"labels\":[\"${component}\""
         while read -r label ; do
-            data_binary="${data_binary},\"${label}\""
+            if [ "$label" ] ; then
+                data_binary="${data_binary},\"${label}\""
+            fi
         done <<< "$backport_pr_labels"
         data_binary="${data_binary}]}"
     else