SAK-48943 Lessons adding new embed code does not update the current video

[st-manu]

https://sakaiproject.atlassian.net/browse/SAK-48943

isImageType calls getExtension, but for scripts, there's no filename, causing a NullPointerException

[ern]

@st-manu what do you think of something simpler, like:

public static String getExtension(String name) {
    String extension = org.springframework.util.StringUtils.getFilenameExtension(name);
    return StringUtils.trimToEmpty(extension).toLowerCase();
}