[SPARK-19748][SQL] refresh function has a wrong order to do cache invalidate and regenerate the inmemory var for InMemoryFileIndex with FileStatusCache

## What changes were proposed in this pull request?

If we refresh a InMemoryFileIndex with a FileStatusCache, it will first use the FileStatusCache to re-generate the cachedLeafFiles etc, then call FileStatusCache.invalidateAll.

While the order to do these two actions is wrong, this lead to the refresh action does not take effect.

```
  override def refresh(): Unit = {
    refresh0()
    fileStatusCache.invalidateAll()
  }

  private def refresh0(): Unit = {
    val files = listLeafFiles(rootPaths)
    cachedLeafFiles =
      new mutable.LinkedHashMap[Path, FileStatus]() ++= files.map(f => f.getPath -> f)
    cachedLeafDirToChildrenFiles = files.toArray.groupBy(_.getPath.getParent)
    cachedPartitionSpec = null
  }
```
## How was this patch tested?
unit test added

Author: windpiger <songjun@outlook.com>

Closes #17079 from windpiger/fixInMemoryFileIndexRefresh.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala
index 7531f0ae02..ee4d0863d9 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala
@@ -66,8 +66,8 @@ class InMemoryFileIndex(
   }
 
   override def refresh(): Unit = {
-    refresh0()
     fileStatusCache.invalidateAll()
+    refresh0()
   }
 
   private def refresh0(): Unit = {