Fix compact mode not filling all available space

This seems to be an unintentional change in compact mode caused by 054f87cae2,
where an if check for "straight line" or "fill width" mode ended up
being removed. But this was needed for availableWidth() to return the
correct width for compact mode, otherwise it got weirdly centered and
ended up with a limited width.

src/libneochat/delegatesizehelper.cpp

@@ -186,6 +186,10 @@ int DelegateSizeHelper::availablePercentageWidth() const
 qreal DelegateSizeHelper::availableWidth() const
 {
     qreal absoluteWidth = maxAvailableWidth() * availablePercentageWidth() * 0.01;
+    // We want to use all available space for a horizontal line.
+    if (m_startPercentWidth == m_endPercentWidth) {
+        return std::round(absoluteWidth);
+    }
     return std::round(std::min(absoluteWidth, maxWidth()));
 }