Cleanup to ImagePage::openShowImage()

- Removed useless $showLink variable and related check since the variable is always defined to true
- Moved $linktext up so that there's no need to use a temporary variable to modify it
- Moved $longDesc down where it's used
- Change "else { if ( ... ) { } }" to elseif for better clarity

Change-Id: I65dcbb76c7f0a0441a6420e76affe797a3dc9c45
Merge "Cleanup to ImagePage::openShowImage()"