Fix gocritic emptyStringTest issues

See,
$ golangci-lint run --disable-all --enable=gocritic --skip-dirs vim25/xml --config ./.golangci.yml | grep emptyStringTest
find/finder.go:256:5: emptyStringTest: replace `len(path) == 0` with `path == ""` (gocritic)
govc/datastore/ls.go:204:8: emptyStringTest: replace `len(p) != 0` with `p != ""` (gocritic)

client_test.go

@@ -46,7 +46,7 @@ func TestNewClient(t *testing.T) {
 		if err != nil {
 			return err
 		}
-		if len(x.Name) == 0 {
+		if x.Name == "" {
 			return errors.New("empty response")
 		}
 		return nil

find/finder.go

@@ -253,7 +253,7 @@ func (f *Finder) managedObjectList(ctx context.Context, path string, tl bool, in
 		fn = f.dcReference
 	}
 
-	if len(path) == 0 {
+	if path == "" {
 		path = "."
 	}
 

govc/datastore/ls.go

@@ -201,7 +201,7 @@ func (o *listOutput) add(r types.HostDatastoreBrowserSearchResults) {
 			}
 
 			for _, p := range path {
-				if len(p) != 0 && p[0] == '.' {
+				if p != "" && p[0] == '.' {
 					return
 				}
 			}

object/datastore_path.go

@@ -31,7 +31,7 @@ type DatastorePath struct {
 // FromString parses a datastore path.
 // Returns true if the path could be parsed, false otherwise.
 func (p *DatastorePath) FromString(s string) bool {
-	if len(s) == 0 {
+	if s == "" {
 		return false
 	}