Correctly handle bindings for the same mod key with and without --release

Correctly handle bindings for the same mod key with and without --release

Before this commit, get_binding() exited on the first match without
marking the rest --release bindings with B_UPON_KEYRELEASE_IGNORE_MODS.

Similarly, once it found a --release binding during a KeyPress event it
would stop searching for a matching key press binding.

Example config, placing the --release line first will trigger the second
problem:

# i3 config file (v4)
bindsym Super_L exec notify-send "press"
# or
# bindcode 133 exec notify-send "press"
bindsym --release Super_L exec notify-send "release"
# or
# bindcode --release 133 exec notify-send "release"

Fixes #2733