The return status of the call to SimpleFileSystem->OpenVolume should be
checked.
It is possible that there is a media change in the device (like CD/DVD
ROM). In such case, the volume root opened and/or the device path opened
previously (also within EfiShellOpenRootByHandle) may be invalid.
This commit adds a check for the result of OpenVolume before subsequently
calling functions like EfiShellGetMapFromDevicePath() &
ConvertEfiFileProtocolToShellHandle().