dshowsrcwrapper: fix regression on device selection

Do not take device_name if a device has been specified. Do not take device_index into account if a device or a device name has been specified.
16 jobs for backport-mr-630-into-1.16-master in 56 minutes and 46 seconds (queued for 1 minute and 37 seconds)
Status Job ID Name Coverage
  Preparation
passed #528447
gst indent

00:00:36

passed #528446
manifest

00:00:44

 
  Build
passed #528453
build cerbero android universal

00:11:10

passed #528454
build cerbero cross win32

00:07:02

passed #528455
build cerbero cross win64

00:09:54

passed #528452
build cerbero fedora x86_64

00:06:59

passed #528457
gst-ios-12.2
build cerbero ios universal

00:38:04

passed #528456
gst-macos-10.14
build cerbero macos x86_64

00:09:15

passed #528448
build fedora x86_64

00:05:53

passed #528449
build nodebug fedora x86_64

00:05:27

passed #528450
build static fedora x86_64

00:12:34

passed #528451
build static nodebug fedora x86_64

00:14:30

 
  Test
passed #528458
check fedora

00:06:21

passed #528459
integration testsuites fedora

00:09:48

passed #528460
valgrind bad

00:09:39

 
  Integrate
passed #528461
android universal examples

00:06:54