ShellPkg: Fix erroneous Status returned by ShellOpenFileByName()

In ShellOpenFileByName() the file is opened using
gEfiShellProtocol->OpenFileByName().
It is supposed that if this call returns an EFI_ERROR, the function
should return that error immediately. However, this return was missing,
and if UnicodeCollationProtocol has not been located by this time, the
Status gets overwritten with LocateProtocol() call result, which
eventually erroneously returns EFI_SUCCESS to the Shell.c, and this
leads to attempt to execute a non-existent startup script, which fails,
and which in turn leads to Shell being unloaded with "Invalid parameter"
error. This patch fixes the bug.

Cc: Tapan Shah <tapandshah@hpe.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>
Reviewed-by: Tapan Shah <tapandshah@hpe.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>