Fix index out of range in patricia tree

Bug #32 reported that there is an index out of range error. This
issue was introduced in 703b087.

Fix #32 and add a test to detect this issue

patricia.go

@@ -161,6 +161,10 @@ func (n *ptNode) match(b []byte, prefix bool) bool {
 		return true
 	}
 
+	if l >= len(b) {
+		return false
+	}
+
 	nextN, ok := n.next[b[l]]
 	if !ok {
 		return false

patricia_test.go

@@ -33,6 +33,13 @@ func testPTree(t *testing.T, strs ...string) {
 		if pt.match(strings.NewReader(s + s)) {
 			t.Errorf("%s matches %s", s+s, s)
 		}
+
+		// The following tests are just to catch index out of
+		// range and off-by-one errors and not the functionality.
+		pt.matchPrefix(strings.NewReader(s[:len(s)-1]))
+		pt.match(strings.NewReader(s[:len(s)-1]))
+		pt.matchPrefix(strings.NewReader(s + "$"))
+		pt.match(strings.NewReader(s + "$"))
 	}
 }
 
@@ -45,5 +52,5 @@ func TestPatriciaNonOverlapping(t *testing.T) {
 }
 
 func TestPatriciaOverlapping(t *testing.T) {
-	testPTree(t, "foo", "far", "farther", "boo", "bar")
+	testPTree(t, "foo", "far", "farther", "boo", "ba", "bar")
 }