Bug in readline when readline-colored-completion-prefix is set

[raphaal]

Hi all,

My version of bash is:
GNU bash, version 5.2.15(1)-release (x86_64-pc-linux-gnu)

When the .inputrc contains:
> colored-completion-prefix on

and LS_COLORS="*.readline-colored-completion-prefix=01;30"

then readline ignores the setting and uses default CYAN color.

After a session of debugging the issue I noticed that there is a 
difference between readline in bash and main readline library:

https://git.savannah.gnu.org/cgit/bash.git/tree/lib/readline/colors.c#n76
#define RL_COLOR_PREFIX_EXTENSION       "readline-colored-completion-prefix"

https://git.savannah.gnu.org/cgit/readline.git/tree/colors.c#n76
#define RL_COLOR_PREFIX_EXTENSION       ".readline-colored-completion-prefix"

(missing dot at the beginning)

It shall be easy to fix

Raphaal