config: display key_delim for config --bool --get-regexp

config: display key_delim for config --bool --get-regexp

The previous logic in show_config was to print the delimiter when the
value was set, but Boolean variables have an implicit value "true" when
they appear with no value in the config file. As a result, we got:

git_Config        --get-regexp '.*\.Boolean'	#1. Ok: example.boolean
git_Config --bool --get-regexp '.*\.Boolean'	#2. NO: example.booleantrue

Fix this by defering the display of the separator until after the value
to display has been computed.

Reported-by: Brian Foster <redacted>
Signed-off-by: Matthieu Moy <redacted>
Signed-off-by: Junio C Hamano <redacted>