add Spout semi-weekly test + vcap/spout hook

this should have catched the:
<https://github.com/CESNET/UltraGrid/issues/487>

and check also for its regression

+ added get_spout (vcap/spout) Doxy

.github/scripts/run_scheduled_tests.sh

@@ -65,6 +65,12 @@ prepare
 ##  - should_timeout - the command is expected to keep running
 ##                     (will be terminated by timeout)
 ##  - run_reflector - instead of uv, pass the args to hd-rum-transcode
+##  - Linux_only    - run just in Linux   runner
+##  - Windows_only  - "   "    "  Windows "
+##  - macOS_only    - "   "    "  macOS   "
+##
+## More platforms with "_only" suffix can be specified, however, eg.
+## Linux_only,macOS_only.
 add_test() {
         eval "test_${test_count}_args=\${1?}"
         eval "test_${test_count}_opts=\${2-}"
@@ -86,6 +92,12 @@ while [ $i -lt $test_count ]; do
                 tool=reflector
                 exec=$run_reflector
         fi
+        # skip one-platform only tests if we are not the target
+        if expr -- "$opts" : '.*_only' >/dev/null; then
+                if ! expr -- "$opts" : ".*$RUNNER_OS" >/dev/null; then
+                        continue
+                fi
+        fi
 
         timeout=5
         timeout $timeout $exec $args

.github/scripts/run_scheduled_tests_data.sh

@@ -8,6 +8,7 @@ add_test -v                                                  # basic sanity test
 add_test --nonexistent-param                   should_fail
 add_test "-d sdl"                              should_timeout
 add_test "-t testcard -c lavc:e=libx265 -f rs -d dummy" should_timeout
+add_test "-t spout:check_lib"                  Windows_only
 
 # reflector
 add_test -v                                    run_reflector # basic sanity test

src/video_capture/spout.cpp

@@ -82,6 +82,11 @@ struct state_vidcap_spout {
         int frames;
 };
 
+/**
+ * @param probe  do not abort if unable to create Spout instance
+ * @returns      shared_ptr with valid Spout instance, unless probe=true
+ *               in which case empty shared_ptr may be returned if error
+ */
 static shared_ptr<SPOUTLIBRARY>
 get_spout(bool probe)
 {
@@ -126,6 +131,23 @@ static void usage()
         }
 }
 
+static void
+check_lib()
+{
+        static shared_ptr<SPOUTLIBRARY> spout  = get_spout(false);
+        constexpr char                  name[] = "test_sender";
+        spout->SetSenderName(name);
+        if (strcmp(spout->GetSenderName(), name) != 0) {
+                // in case of the GH-487 problem, it actually doesn't reach
+                // here but segfaults on the returned name from the library
+                // because (const char *) 0x1 is returned
+                fprintf(stderr, "Unexpected sender name: %s (exp: %s)\n",
+                        spout->GetSenderName(), name);
+                abort();
+        }
+        printf("SpoutLibrary vtable doesn't seem to be corrupted.\n");
+}
+
 static int vidcap_spout_init(struct vidcap_params *params, void **state)
 {
         if ((vidcap_params_get_flags(params) & VIDCAP_FLAG_AUDIO_ANY) != 0U) {
@@ -147,6 +169,10 @@ static int vidcap_spout_init(struct vidcap_params *params, void **state)
                         usage();
                         ret = VIDCAP_INIT_NOERR;
                         break;
+                } else if (strcmp(item, "check_lib") == 0) {
+                        check_lib();
+                        ret = VIDCAP_INIT_NOERR;
+                        break;
                 } else if (strstr(item, "name=") == item) {
                         char *name = item + strlen("name=");
                         if (strstr(name, "urlencoded=") == name) {