[libcalamaresui] Relax validity check in branding

- A size of 64em has a value less than 1024, which is the minimum
   size **in pixels**. The check doesn't make sense as-is and would
   have to take the unit into account. Leave that to clients of
   branding (e.g. CalamaresWindow, which already does this).

src/libcalamaresui/Branding.cpp

@@ -336,9 +336,9 @@ Branding::initSimpleSettings( const YAML::Node& doc )
             m_windowHeight = WindowDimension( dimensionNames, l[1] );
         }
     }
-    if ( !m_windowWidth.isValid() || m_windowWidth.value() < CalamaresUtils::windowMinimumWidth )
+    if ( !m_windowWidth.isValid() )
         m_windowWidth = WindowDimension( CalamaresUtils::windowPreferredWidth, WindowDimensionUnit::Pixies );
-    if ( !m_windowHeight.isValid() || m_windowHeight.value() < CalamaresUtils::windowMinimumHeight )
+    if ( !m_windowHeight.isValid() )
         m_windowHeight = WindowDimension( CalamaresUtils::windowPreferredHeight, WindowDimensionUnit::Pixies );
 }