[SPARK-48991][SQL] Move path initialization into try-catch block in FileStreamSink.hasMetadata

### What changes were proposed in this pull request?

This pull request proposed to move path initialization into try-catch block in FileStreamSink.hasMetadata. Then, exceptions from invalid paths can be handled consistently like other path-related exceptions in the current try-catch block. At last, we can make the errors fall into the correct code branches to be handled

### Why are the changes needed?

bugfix for improperly handled exceptions in FileStreamSink.hasMetadata

### Does this PR introduce _any_ user-facing change?

no, an invalid path is still invalid, but fails in the correct places

### How was this patch tested?

new test

### Was this patch authored or co-authored using generative AI tooling?
no

Closes #47471 from yaooqinn/SPARK-48991.

Authored-by: Kent Yao <yao@apache.org>
Signed-off-by: Kent Yao <yao@apache.org>
(cherry picked from commit d68cde8)
Signed-off-by: Kent Yao <yao@apache.org>

Author: yaooqinn

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSink.scala

@@ -48,8 +48,8 @@ object FileStreamSink extends Logging {
 
     path match {
       case Seq(singlePath) =>
-        val hdfsPath = new Path(singlePath)
         try {
+          val hdfsPath = new Path(singlePath)
           val fs = hdfsPath.getFileSystem(hadoopConf)
           if (fs.isDirectory(hdfsPath)) {
             val metadataPath = getMetadataLogPath(fs, hdfsPath, sqlConf)

sql/core/src/test/scala/org/apache/spark/sql/streaming/FileStreamSinkSuite.scala

@@ -650,6 +650,19 @@ abstract class FileStreamSinkSuite extends StreamTest {
       }
     }
   }
+
+  test("SPARK-48991: Move path initialization into try-catch block") {
+    val logAppender = new LogAppender("Assume no metadata directory.")
+    Seq(null, "", "file:tmp").foreach { path =>
+      withLogAppender(logAppender) {
+        assert(!FileStreamSink.hasMetadata(Seq(path), spark.sessionState.newHadoopConf(), conf))
+      }
+
+      assert(logAppender.loggingEvents.map(_.getMessage.getFormattedMessage).contains(
+        "Assume no metadata directory. Error while looking for metadata directory in the path:" +
+        s" $path."))
+    }
+  }
 }
 
 object PendingCommitFilesTrackingManifestFileCommitProtocol {