fix position handling in geoclue2 plugin

fix position handling in geoclue2 plugin

Origin: upstream, https://code.qt.io/cgit/qt/qtpositioning.git/commit/?id=70b7818e1fc585f8
Last-Update: 2021-11-10

The pre-existing code was incorrect due to the operation priority.
The result of the comparison was assigned to the variables, so they
were always initialized with 0 or 1 instead of real values.

Also use std::numeric_limits<double>::lowest(), because the altitude
can have a negative value (when we are below sea level).

Gbp-Pq: Name geoclue2_fix_position_handling.diff