specify file parameter

lazpaint/release/debian/applications/lazpaint.desktop

@@ -4,7 +4,7 @@ Name[fr]=LazPaint
 Comment=LazPaint
 Comment[fr]=LazPaint
 Icon=lazpaint
-Exec=lazpaint
+Exec=lazpaint %f
 Terminal=false
 Type=Application
 Categories=Graphics