fix asprintf warnings

Fix recently introduced compiler warnings:

desktop-shell/shell.c: In function 'shell_configuration':
desktop-shell/shell.c:588:10: warning: ignoring return value of
'asprintf', declared with attribute warn_unused_result [-Wunused-result]

src/screenshooter.c: In function ‘screenshooter_binding’:
src/screenshooter.c:291:10: warning: ignoring return value of
‘asprintf’, declared with attribute warn_unused_result [-Wunused-result]

src/text-backend.c: In function ‘text_backend_configuration’:
src/text-backend.c:944:10: warning: ignoring return value of ‘asprintf’,
declared with attribute warn_unused_result [-Wunused-result]

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

desktop-shell/shell.c

@@ -575,6 +575,7 @@ shell_configuration(struct desktop_shell *shell)
 	struct weston_config_section *section;
 	int duration;
 	char *s, *client;
+	int ret;
 
 	section = weston_config_get_section(shell->compositor->config,
 					    "screensaver", NULL, NULL);
@@ -585,8 +586,10 @@ shell_configuration(struct desktop_shell *shell)
 
 	section = weston_config_get_section(shell->compositor->config,
 					    "shell", NULL, NULL);
-	asprintf(&client, "%s/%s", weston_config_get_libexec_dir(),
-				   WESTON_SHELL_CLIENT);
+	ret = asprintf(&client, "%s/%s", weston_config_get_libexec_dir(),
+		       WESTON_SHELL_CLIENT);
+	if (ret < 0)
+		client = NULL;
 	weston_config_section_get_string(section,
 					 "client", &s, client);
 	free(client);

src/screenshooter.c

@@ -287,9 +287,15 @@ screenshooter_binding(struct weston_seat *seat, uint32_t time, uint32_t key,
 {
 	struct screenshooter *shooter = data;
 	char *screenshooter_exe;
+	int ret;
 
-	asprintf(&screenshooter_exe, "%s/%s", weston_config_get_libexec_dir(),
-					      "/weston-screenshooter");
+	ret = asprintf(&screenshooter_exe, "%s/%s",
+		       weston_config_get_libexec_dir(),
+		       "/weston-screenshooter");
+	if (ret < 0) {
+		weston_log("Could not construct screenshooter path.\n");
+		return;
+	}
 
 	if (!shooter->client)
 		shooter->client = weston_client_launch(shooter->ec,

src/text-backend.c

@@ -938,11 +938,14 @@ text_backend_configuration(struct text_backend *text_backend)
 {
 	struct weston_config_section *section;
 	char *client;
+	int ret;
 
 	section = weston_config_get_section(text_backend->compositor->config,
 					    "input-method", NULL, NULL);
-	asprintf(&client, "%s/weston-keyboard",
-		 weston_config_get_libexec_dir());
+	ret = asprintf(&client, "%s/weston-keyboard",
+		       weston_config_get_libexec_dir());
+	if (ret < 0)
+		client = NULL;
 	weston_config_section_get_string(section, "path",
 					 &text_backend->input_method.path,
 					 client);