[Patch] ShellPkg/TftpDynamicCommand: Fix the potential assertion and memory leak issue.

[Jiaxin Wu <Jiaxin.wu@intel.com>]

From: Jiaxin Wu <jiaxin.wu@intel.com>

This patch is to fix the issue reported from
https://bugzilla.tianocore.org/show_bug.cgi?id=925.

DataSize variable was not assigned the value if ShellOpenFileByName returns error.
In the such a case, it should not be used to FreePages. Instead, DataSize can be
used to record the file size once DownloadFile successfully.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
---
 ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c b/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
index e2491cd54c..44be6d4e76 100644
--- a/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
+++ b/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
@@ -517,10 +517,12 @@ RunTftp (
         mTftpHiiHandle, RemoteFilePath, NicName, Status
       );
       goto NextHandle;
     }
 
+    DataSize = FileSize;
+
     if (!EFI_ERROR (ShellFileExists (LocalFilePath))) {
       ShellDeleteFileByName (LocalFilePath);
     }
 
     Status = ShellOpenFileByName (
@@ -537,11 +539,10 @@ RunTftp (
         mTftpHiiHandle, L"tftp", LocalFilePath
       );
       goto NextHandle;
     }
 
-    DataSize = FileSize;
     Status = ShellWriteFile (FileHandle, &FileSize, Data);
     if (!EFI_ERROR (Status)) {
       ShellStatus = SHELL_SUCCESS;
     } else {
       ShellPrintHiiEx (
-- 
2.17.1.windows.2