HDFS-17917. Fix empty block list enqueue in markedDeleteQueue

[magnuma3]

Description of PR

When deleting empty directory, empty list is added to markedDeleteQueue.
I think this is unnecessary. and markedDeleteQueue.size() is O(n) operation, so it is costly.

How was this patch tested?

unit test

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
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• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

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[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	18m 54s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ trunk Compile Tests _
+1 💚	mvninstall	48m 32s		trunk passed
+1 💚	compile	1m 43s		trunk passed with JDK Ubuntu-21.0.10+7-Ubuntu-124.04
+1 💚	compile	1m 48s		trunk passed with JDK Ubuntu-17.0.18+8-Ubuntu-124.04.1
+1 💚	checkstyle	1m 49s		trunk passed
+1 💚	mvnsite	1m 54s		trunk passed
+1 💚	javadoc	1m 23s		trunk passed with JDK Ubuntu-21.0.10+7-Ubuntu-124.04
+1 💚	javadoc	1m 28s		trunk passed with JDK Ubuntu-17.0.18+8-Ubuntu-124.04.1
+1 💚	spotbugs	4m 22s		trunk passed
+1 💚	shadedclient	38m 5s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 24s		the patch passed
+1 💚	compile	1m 15s		the patch passed with JDK Ubuntu-21.0.10+7-Ubuntu-124.04
+1 💚	javac	1m 15s		the patch passed
+1 💚	compile	1m 19s		the patch passed with JDK Ubuntu-17.0.18+8-Ubuntu-124.04.1
+1 💚	javac	1m 19s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
-0 ⚠️	checkstyle	1m 18s	/results-checkstyle-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs-project/hadoop-hdfs: The patch generated 2 new + 169 unchanged - 0 fixed = 171 total (was 169)
+1 💚	mvnsite	1m 27s		the patch passed
+1 💚	javadoc	0m 59s		the patch passed with JDK Ubuntu-21.0.10+7-Ubuntu-124.04
+1 💚	javadoc	1m 2s		the patch passed with JDK Ubuntu-17.0.18+8-Ubuntu-124.04.1
+1 💚	spotbugs	4m 2s		the patch passed
+1 💚	shadedclient	37m 4s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	260m 56s		hadoop-hdfs in the patch passed.
+1 💚	asflicense	0m 53s		The patch does not generate ASF License warnings.
		429m 30s

Subsystem	Report/Notes
Docker	ClientAPI=1.54 ServerAPI=1.54 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8475/1/artifact/out/Dockerfile
GITHUB PR	#8475
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux edc70f84b773 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14 20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 83814a6
Default Java	Ubuntu-17.0.18+8-Ubuntu-124.04.1
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.10+7-Ubuntu-124.04 /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.18+8-Ubuntu-124.04.1
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8475/1/testReport/
Max. process+thread count	2433 (vs. ulimit of 10000)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8475/1/console
versions	git=2.43.0 maven=3.9.11 spotbugs=4.9.7
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