leaflet: Init mode transition positions to the final values

Set the target and current mode transition positions to the final 1.0
value instead of the initial 0.0 one.

This fixes an inconsistency on initially unfolded leaflets as they would
be drawn in their folded state with no animation triggered to transition
to the final state as the target and the current values were the same.
1 job for leaflet-mode-transition-init in 1 minute and 58 seconds
Status Job ID Name Coverage
  Build
passed #1603
librem5
build-debian

00:01:58