After modifying an image, Gwenview displays a toolbar above the image
with options for saving. When resizing the sidebar or the window
horizontally and thus taking away space, some buttons and labels could
be hidden. In particular the Next modified image link was not
accessible anymore.

This can be solved by eliding the labels instead.

To center the whole group in the middle properly and due to deficiencies
in KSqueezedLabel the patch is a bit more complex, but should be
fairly self-contained.

Modify a single and multiple images, navigate around and check that all
buttons and labels in the save bar still work correctly. Resizing the
sidebar should elide all labels evenly, so even with a narrow window
size both navigation buttons should be visible at all times.

Before/After: