qemu_driver: increase recorded counter for disk block stats

Commit <318d807a0bd3372b634d1952b559c5c627ccfa5b> added a fix to skip
most of the block stat code to not log error message for missing storage
sources but forgot to increase the recordnr counter.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -18414,8 +18414,14 @@ qemuDomainGetStatsBlockExportDisk(virDomainDiskDefPtr disk,
         VIR_INFO("optional disk '%s' source file is missing, "
                  "skip getting stats", disk->dst);
 
-        return qemuDomainGetStatsBlockExportHeader(disk, disk->src, *recordnr,
-                                                   params);
+        if (qemuDomainGetStatsBlockExportHeader(disk, disk->src, *recordnr,
+                                                params) < 0) {
+            return -1;
+        }
+
+        (*recordnr)++;
+
+        return 0;
     }
 
     /* vhost-user disk doesn't support getting block stats */