[PATCH] completion: Allow dash as the first character for __git_ps1

If the argument for `__git_ps1` begins with a dash, `printf` tries to
interpret it as an option which results in an error message.
The problem is solved by adding '--' before the argument to tell
`printf` to not interpret the following argument as an option.
Adding '--' directly to the argument does not help because the argument
is enclosed by double quotes.

Signed-off-by: Christian Hammerl <redacted>
---
 contrib/completion/git-completion.bash |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 91c7acb..61ff152 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash

@@ -313,7 +313,7 @@ __git_ps1 ()
 		fi
 
 		local f="$w$i$s$u"
-		printf "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r$p"
+		printf -- "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r$p"
 	fi
 }
 

-- 
1.7.9