git config get subcommand mishandles parsing colors

It was reported that the new git config get subcommand is broken with --type=color. There's two bugs:

• git color get --type=color --default=reset "" is broken because we cannot handle that the config key is empty. The expectation is that this should simply parse "reset" into an ANSI color escape sequence.
• git color get --type=color spawns a pager, which doesn't make any sense.