rtsp source: fix crash in case a PLAY request fails

go.mod

@@ -4,7 +4,7 @@ go 1.17
 
 require (
 	code.cloudfoundry.org/bytefmt v0.0.0-20211005130812-5bb3c17173e5
-	github.com/aler9/gortsplib v0.0.0-20220130155047-8c02b12955f8
+	github.com/aler9/gortsplib v0.0.0-20220131085902-9603037fb337
 	github.com/asticode/go-astits v1.10.0
 	github.com/fsnotify/fsnotify v1.4.9
 	github.com/gin-gonic/gin v1.7.2

go.sum

@@ -4,8 +4,8 @@ github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751 h1:JYp7IbQjafo
 github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20190924025748-f65c72e2690d h1:UQZhZ2O0vMHr2cI+DC1Mbh0TJxzA3RcLoMsFw+aXw7E=
 github.com/alecthomas/units v0.0.0-20190924025748-f65c72e2690d/go.mod h1:rBZYJk541a8SKzHPHnH3zbiI+7dagKZ0cgpgrD7Fyho=
-github.com/aler9/gortsplib v0.0.0-20220130155047-8c02b12955f8 h1:kGq65HZMjRo2ay0eJO/MxkEhD2DcDTkcX4qCgsjUkSs=
-github.com/aler9/gortsplib v0.0.0-20220130155047-8c02b12955f8/go.mod h1:fyQrQyHo8QvdR/h357tkv1g36VesZlzEPsdAu2VrHHc=
+github.com/aler9/gortsplib v0.0.0-20220131085902-9603037fb337 h1:+cgIhG3FjZLT6y9z/0La8WDWoLkrC6HANzIL7fdMq3k=
+github.com/aler9/gortsplib v0.0.0-20220131085902-9603037fb337/go.mod h1:fyQrQyHo8QvdR/h357tkv1g36VesZlzEPsdAu2VrHHc=
 github.com/aler9/rtmp v0.0.0-20210403095203-3be4a5535927 h1:95mXJ5fUCYpBRdSOnLAQAdJHHKxxxJrVCiaqDi965YQ=
 github.com/aler9/rtmp v0.0.0-20210403095203-3be4a5535927/go.mod h1:vzuE21rowz+lT1NGsWbreIvYulgBpCGnQyeTyFblUHc=
 github.com/asticode/go-astikit v0.20.0 h1:+7N+J4E4lWx2QOkRdOf6DafWJMv6O4RRfgClwQokrH8=