Fix "Could not find v4l2 muxer"

The AVOutputFormat name is a comma-separated list. In theory, possible
names for V4L2 are:

    - "video4linux2,v4l2"
    - "v4l2,video4linux2"
    - "v4l2"
    - "video4linux2"

To find the muxer in all cases, we must request exactly one muxer name
at a time.

PR #2718 <#2718>

Co-authored-by: Romain Vimont <rom@rom1v.com>
Signed-off-by: Romain Vimont <rom@rom1v.com>

app/src/v4l2_sink.c

@@ -183,8 +183,11 @@ sc_v4l2_sink_open(struct sc_v4l2_sink *vs) {
         goto error_mutex_destroy;
     }
 
-    // FIXME
-    const AVOutputFormat *format = find_muxer("video4linux2,v4l2");
+    const AVOutputFormat *format = find_muxer("v4l2");
+    if (!format) {
+        // Alternative name
+        format = find_muxer("video4linux2");
+    }
     if (!format) {
         LOGE("Could not find v4l2 muxer");
         goto error_cond_destroy;