Fix truecolor escapes, when both bg and fg are set

for example
echo -e "\e[48;2;255;0;0m\e[38;2;0;0;255m test "
should render on red bg with blue fg

also now elinks works correctly when using 'truecolor' option
in preferences

Signed-off-by: Amadeusz Sławiński <[email protected]>