fix nil-pointer dereference in detailed config log

Closes #719.

Signed-off-by: Peter Schultz <peter.schultz@classmarkets.com>

Author: pschultz

CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Changelog
 
+### Unreleased
+
+#### Bug Fixes
+
+* [Issue #719](https://github.com/fabiolb/fabio/issues/719): Fix detailed config log
+
 ### [v1.5.12](https://github.com/fabiolb/fabio/releases/tag/v1.5.12) - 11 Oct 2019
 
 #### Breaking Changes

route/table.go

@@ -501,7 +501,7 @@ func (t Table) String() string {
 
 // Dump returns the routing table as a detailed
 func (t Table) Dump() string {
-	var w *bytes.Buffer
+	w := new(bytes.Buffer)
 
 	hosts := []string{}
 	for k := range t {

route/table_test.go

@@ -731,3 +731,32 @@ func TestNewTableCustom(t *testing.T) {
 		t.FailNow()
 	}
 }
+
+func TestTable_Dump(t *testing.T) {
+	s := `
+	route add svc / http://foo.com:800
+	route add svc /foo http://foo.com:900
+	route add svc abc.com/ http://foo.com:1000
+	`
+
+	tbl, err := NewTable(bytes.NewBufferString(s))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := `+-- host=
+|   |-- path=/foo
+|   |    +-- addr=foo.com:900 weight 1.00 slots 1/1
+|   +-- path=/
+|       +-- addr=foo.com:800 weight 1.00 slots 1/1
++-- host=abc.com
+    +-- path=/
+        +-- addr=foo.com:1000 weight 1.00 slots 1/1
+`
+
+	got := tbl.Dump()
+
+	if want != got {
+		t.Errorf("Unexpected Dump() output:\nwant:\n%s\ngot:\n%s\n", want, got)
+	}
+}