fix: incorrect truncation of CSS resource reads (#4678)

#### What type of PR is this?
/kind bug
/area core
/milestone 2.10.x

#### What this PR does / why we need it:
修复插件 css bundle 内容被错误拆分导致无法加载的问题

#### Which issue(s) this PR fixes:
Fixes #4677

#### Does this PR introduce a user-facing change?
```release-note
修复插件 css bundle 内容被错误拆分导致无法加载的问题
```

application/src/main/java/run/halo/app/core/extension/service/impl/PluginServiceImpl.java

@@ -26,7 +26,6 @@ import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
 import org.springframework.stereotype.Component;
 import org.springframework.util.Assert;
-import org.springframework.util.StreamUtils;
 import org.springframework.web.server.ServerWebInputException;
 import reactor.core.Exceptions;
 import reactor.core.publisher.Flux;
@@ -179,9 +178,15 @@ public class PluginServiceImpl implements PluginService {
                 return BundleResourceUtils.getJsBundleResource(pluginManager, pluginName,
                     BundleResourceUtils.CSS_BUNDLE);
             })
-            .flatMap(resource -> DataBufferUtils.read(resource,
-                DefaultDataBufferFactory.sharedInstance, StreamUtils.BUFFER_SIZE)
-            );
+            .flatMap(resource -> {
+                try {
+                    return DataBufferUtils.read(resource, DefaultDataBufferFactory.sharedInstance,
+                        (int) resource.contentLength());
+                } catch (IOException e) {
+                    log.error("Failed to read plugin css bundle resource", e);
+                    return Flux.empty();
+                }
+            });
     }
 
     @Override