input_plugin: method init() returns errors with GError

Not used by any plugin currently, but this eliminates the g_error()
call in input_plugin_config(), so it's worth it.

test/dump_playlist.c

@@ -74,7 +74,12 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	input_stream_global_init();
+	if (!input_stream_global_init(&error)) {
+		g_warning("%s", error->message);
+		g_error_free(error);
+		return 2;
+	}
+
 	playlist_list_global_init();
 
 	/* open the playlist */

test/read_tags.c

@@ -129,6 +129,7 @@ print_tag(const struct tag *tag)
 
 int main(int argc, char **argv)
 {
+	GError *error = NULL;
 	const char *decoder_name, *path;
 	const struct decoder_plugin *plugin;
 	struct tag *tag;
@@ -147,7 +148,12 @@ int main(int argc, char **argv)
 	decoder_name = argv[1];
 	path = argv[2];
 
-	input_stream_global_init();
+	if (!input_stream_global_init(&error)) {
+		g_warning("%s", error->message);
+		g_error_free(error);
+		return 2;
+	}
+
 	decoder_plugin_init_all();
 
 	plugin = decoder_plugin_from_name(decoder_name);

test/run_decoder.c

@@ -138,6 +138,7 @@ decoder_tag(G_GNUC_UNUSED struct decoder *decoder,
 
 int main(int argc, char **argv)
 {
+	GError *error = NULL;
 	bool ret;
 	const char *decoder_name;
 	struct decoder decoder;
@@ -152,7 +153,12 @@ int main(int argc, char **argv)
 
 	g_log_set_default_handler(my_log_func, NULL);
 
-	input_stream_global_init();
+	if (!input_stream_global_init(&error)) {
+		g_warning("%s", error->message);
+		g_error_free(error);
+		return 2;
+	}
+
 	decoder_plugin_init_all();
 
 	decoder.plugin = decoder_plugin_from_name(decoder_name);

test/run_input.c

@@ -41,6 +41,7 @@ my_log_func(const gchar *log_domain, G_GNUC_UNUSED GLogLevelFlags log_level,
 int main(int argc, char **argv)
 {
 	struct input_stream is;
+	GError *error = NULL;
 	bool success;
 	char buffer[4096];
 	size_t num_read;
@@ -60,7 +61,12 @@ int main(int argc, char **argv)
 
 	tag_pool_init();
 	config_global_init();
-	input_stream_global_init();
+
+	if (!input_stream_global_init(&error)) {
+		g_warning("%s", error->message);
+		g_error_free(error);
+		return 2;
+	}
 
 	/* open the stream and wait until it becomes ready */