[fix] fix doc pulling error (apache#6016)

Author: Aias00

shenyu-admin/src/main/java/org/apache/shenyu/admin/service/manager/impl/LoadServiceDocEntryImpl.java

@@ -97,9 +97,13 @@ public synchronized void loadApiDocument() {
             LOG.info("load api document No service registered.");
             return;
         }
-        final Set<UpstreamInstance> currentServices = new HashSet<>(serviceList);
-        LOG.info("load api document, serviceList={}", JsonUtils.toJson(currentServices));
-        pullSwaggerDocService.pullApiDocument(currentServices);
+        try {
+            final Set<UpstreamInstance> currentServices = new HashSet<>(serviceList);
+            LOG.info("load api document, serviceList={}", JsonUtils.toJson(currentServices));
+            pullSwaggerDocService.pullApiDocument(currentServices);
+        } catch (Exception e) {
+            LOG.error("load api document error", e);
+        }
     }
 
     @Override