pactl: fix parsing of percentages with decimal points

The logic for detecting which type of volume was given incorrectly interpreted any value with a decimal as a VOL_LINEAR. It also could set multiple flags, which would put the flags variable into an indeterminate state. Additionally, the flags stack variable was uninitialized which could also lead to an indeterminate flag state.

Percentages are now prioritized over all other types, and only one type flag can be set.

Issue reported on ML: https://lists.freedesktop.org/archives/pulseaudio-discuss/2022-June/032275.html