TFTP : tftp fix for full volume case

Issue :
When storage media is full, tftp was resulting in ASSERT
MdeModulePkg/Core/Dxe/Mem/Page.c, because number of pages
was zero.

Reason:
While doing tftp, function call ShellWriteFile was modifying
FileSize variable. In case of full disk it was coming out to be
Zero.

Fix:
Storage the original filesize in local variable, and use this
variable while freeing the pages.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Udit Kumar <udit.kumar@nxp.com>
Signed-off-by: Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
Signed-off-by: Vabhav Sharma <vabhav.sharma@nxp.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

ShellPkg/Library/UefiShellTftpCommandLib/Tftp.c

@@ -284,6 +284,7 @@ ShellCommandRunTftp (
   EFI_HANDLE              Mtftp4ChildHandle;
   EFI_MTFTP4_PROTOCOL     *Mtftp4;
   UINTN                   FileSize;
+  UINTN                   DataSize;
   VOID                    *Data;
   SHELL_FILE_HANDLE       FileHandle;
   UINT16                  BlockSize;
@@ -294,6 +295,7 @@ ShellCommandRunTftp (
   AsciiRemoteFilePath = NULL;
   Handles             = NULL;
   FileSize            = 0;
+  DataSize            = 0;
   BlockSize           = MTFTP_DEFAULT_BLKSIZE;
 
   //
@@ -537,6 +539,7 @@ ShellCommandRunTftp (
       goto NextHandle;
     }
 
+    DataSize = FileSize;
     Status = ShellWriteFile (FileHandle, &FileSize, Data);
     if (!EFI_ERROR (Status)) {
       ShellStatus = SHELL_SUCCESS;
@@ -551,7 +554,7 @@ ShellCommandRunTftp (
     NextHandle:
 
     if (Data != NULL) {
-      gBS->FreePages ((EFI_PHYSICAL_ADDRESS)(UINTN)Data, EFI_SIZE_TO_PAGES (FileSize));
+      gBS->FreePages ((EFI_PHYSICAL_ADDRESS)(UINTN)Data, EFI_SIZE_TO_PAGES (DataSize));
     }
 
     CloseProtocolAndDestroyServiceChild (