umpf: support piping yes into umpf

When building or tagging an umpf, umpf can ask which branch to use when
multiple are available. Piping yes(1) into umpf in this case doesn't
work, because the variable populated by read in that case is left empty.

Handle this case to reduce user confusion.

Signed-off-by: Ahmad Fatoum <[email protected]>

Author: a3f

umpf

@@ -445,6 +445,10 @@ find_branch_rev() {
 			i=$((i+1))
 		done
 		read -e -i ${def} -p "branch number: " i
+		# if yes(1) is piped in, i is not populated
+		if [ -z "$i" ]; then
+			i="${def}"
+		fi
 		nice_branch "${branches[$i]}"
 		remote="${replies[1]:-refs/heads}/"
 		if [ -z "${GIT_REMOTE}" ]; then