x11/libqtxdg: update to 3.7.1

libqtxdg-3.7.1 / 2021-04-16
===========================
  - Fixed compilation against Qt < 5.14.
  - Added a nullity check for paint device.

libqtxdg-3.7.0 / 2021-04-15
===========================
  - Removed deprecated XdgDesktopFileCache.
  - Handled Qt 5.15 deprecations.
  - Use "= default" for trivial constructors/destructors.
  - Improved readability in container emptiness check.
  - Ported QStringRef to QStringView.
  - Moved to Qt5 signal/slot syntax.
  - Added XTerm as a runtime dependency.
  - Allow non-detached starting in xdgdesktopfile.
  - Use QSvgRenderer for SVG icons.

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