completion: small optimization

No need to calculate a new $c with a space if we are not going to do
anything it with it.

There should be no functional changes, except that a word "foo " with no
suffixes can't be matched. But $cur cannot have a space at the end
anyway. So it's safe.

Based on the code from SZEDER Gábor.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -210,11 +210,11 @@ __gitcomp ()
 		local c i=0 IFS=$' \t\n'
 		for c in $1; do
 			c="$c${4-}"
-			case $c in
-			--*=*|*.) ;;
-			*) c="$c " ;;
-			esac
 			if [[ $c == "$cur_"* ]]; then
+				case $c in
+				--*=*|*.) ;;
+				*) c="$c " ;;
+				esac
 				COMPREPLY[i++]="${2-}$c"
 			fi
 		done