Daniel Brötzmann authored Jun 21, 2019 and Philipp Hörist committed Jun 21, 2019

When using one window mode, we get the allocated size of our message control
notebook and save it before closing. The allocated width of our notebook does
not include the background-size of the Paned's separator. Calculating width
by subtracting roster_hpaned_position from allocated width of our window fixes
this.