Fixed panic when Router#Find fails on Param paths

Fixed panic when Router#Find fails to find a route that could match a
Param route that only have children routes and no root route.
e.g
/create
/:id/edit
/:id/active

Finding /creates results in panic because the router tree node that
belongs to the param route :id don't have pnames on it. The childrens of
:id (:id/edit and :id/active) have the pnames properly set, but those
are not processed because /creates don't match on those paths.

Author: pafuent

go.sum

@@ -15,6 +15,7 @@ github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHX
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
@@ -46,6 +47,7 @@ golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e h1:FDhOuMEY4JVRztM/gsbk+IKUQ8kj74bxZrgw87eMMVc=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

router.go

@@ -428,7 +428,9 @@ func (r *Router) Find(method, path string, c Context) {
 				pos := strings.IndexByte(ns, '/')
 				if pos == -1 {
 					// If no slash is remaining in search string set param value
-					pvalues[len(cn.pnames)-1] = search
+					if len(cn.pnames) > 0 {
+						pvalues[len(cn.pnames)-1] = search
+					}
 					break
 				} else if pos > 0 {
 					// Otherwise continue route processing with restored next node

router_test.go

@@ -1298,6 +1298,40 @@ func TestRouterParam1466(t *testing.T) {
 	assert.Equal(t, 0, c.response.Status)
 }
 
+// Issue #1653
+func TestRouterPanicWhenParamNoRootOnlyChildsFailsFind(t *testing.T) {
+	e := New()
+	r := e.router
+
+	r.Add(http.MethodGet, "/users/create", handlerHelper("create", 1))
+	r.Add(http.MethodGet, "/users/:id/edit", func(c Context) error {
+		return nil
+	})
+	r.Add(http.MethodGet, "/users/:id/active", func(c Context) error {
+		return nil
+	})
+
+	c := e.NewContext(nil, nil).(*context)
+	r.Find(http.MethodGet, "/users/alice/edit", c)
+	assert.Equal(t, "alice", c.Param("id"))
+
+	c = e.NewContext(nil, nil).(*context)
+	r.Find(http.MethodGet, "/users/bob/active", c)
+	assert.Equal(t, "bob", c.Param("id"))
+
+	c = e.NewContext(nil, nil).(*context)
+	r.Find(http.MethodGet, "/users/create", c)
+	c.Handler()(c)
+	assert.Equal(t, 1, c.Get("create"))
+	assert.Equal(t, "/users/create", c.Get("path"))
+
+	//This panic before the fix for Issue #1653
+	c = e.NewContext(nil, nil).(*context)
+	r.Find(http.MethodGet, "/users/createNotFound", c)
+	he := c.Handler()(c).(*HTTPError)
+	assert.Equal(t, http.StatusNotFound, he.Code)
+}
+
 func benchmarkRouterRoutes(b *testing.B, routes []*Route) {
 	e := New()
 	r := e.router