Florian Müllner authored Oct 12, 2020 and Georges Basile Stavracas Neto committed Oct 14, 2020

Commit 033f0d11 added a fallback in case the tile monitor wasn't
set before, but didn't actually check for a previously set value.
As a result, the "fallback" is not set unconditionally, which may
differ from the expected monitor: The tile monitor is determined
by the pointer position, while the window's monitor is the one
where the biggest part of the window resides on.

#1389