minimal/do whichdo: should print ../default.do if ../$1.do exists.

It would be incorrect to print ../$1.do (we only use $1.do in the
*current* directly, not prefix dirs; we only use default*.do in
those).  However, when we found ../default.do, we forgot to print it,
because of a silly logic error.

t/260-whichdo/all.do

@@ -1 +1 @@
-redo exists nonexists
+redo exists nonexists defaults

t/260-whichdo/defaults.do

@@ -0,0 +1,16 @@
+exec >&2
+
+a=$(cd fakesub2 && redo-whichdo d/snork)
+# if sh doesn't abort after the above, then it found a .do file as expected
+
+b=$(cat <<EOF
+d/snork.do
+d/default.do
+default.do
+EOF
+)
+
+if [ "$a" != "$b" ]; then
+    printf 'redo-whichdo mismatch.\n\ngot:\n%s\n\nexpected:\n%s\n' "$a" "$b"
+    exit 11
+fi

t/260-whichdo/fakesub2/default.do

@@ -0,0 +1 @@
+:

t/260-whichdo/fakesub2/snork.do

@@ -0,0 +1 @@
+: