storage: Do not break the whole vol lookup process in the middle

* src/storage/storage_driver.c: As virStorageVolLookupByPath lookups
all the pool objs of the drivers, breaking when failing on getting
the stable path of the pool will just breaks the whole lookup process,
it can cause the API fails even if the vol exists indeed. It won't get
any benefit. This patch is to fix it.

src/storage/storage_driver.c

@@ -1247,14 +1247,14 @@ storageVolumeLookupByPath(virConnectPtr conn,
 
             stable_path = virStorageBackendStablePath(driver->pools.objs[i],
                                                       cleanpath);
-            /*
-             * virStorageBackendStablePath already does
-             * virStorageReportError if it fails; we just need to keep
-             * propagating the return code
-             */
             if (stable_path == NULL) {
+                /* Don't break the whole lookup process if it fails on
+                 * getting the stable path for some of the pools.
+                 */
+                VIR_WARN("Failed to get stable path for pool '%s'",
+                         driver->pools.objs[i]->def->name);
                 virStoragePoolObjUnlock(driver->pools.objs[i]);
-                goto cleanup;
+                continue;
             }
 
             vol = virStorageVolDefFindByPath(driver->pools.objs[i],
@@ -1274,7 +1274,6 @@ storageVolumeLookupByPath(virConnectPtr conn,
         virStorageReportError(VIR_ERR_NO_STORAGE_VOL,
                               "%s", _("no storage vol with matching path"));
 
-cleanup:
     VIR_FREE(cleanpath);
     storageDriverUnlock(driver);
     return ret;