multi-resource: Check for no digits in time description

strtoul(nptr, endptr, ...) will set *endptr to nptr in the case of where
no digits were read from the string.  E.g. "foo:bar" should trigger an
error, instead of being read as "0:0" and allowed through.

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>

clients/multi-resource.c

@@ -434,12 +434,13 @@ create_device(struct display *display, const char *time_desc, int type)
 
 	errno = 0;
 	start_time = strtoul(time_desc, &tail, 10);
-	if (errno)
+	if (errno || tail == time_desc)
 		goto error;
 
 	if (*tail == ':') {
-		end_time = strtoul(tail + 1, &tail, 10);
-		if (errno || *tail != '\0')
+		time_desc = tail + 1;
+		end_time = strtoul(time_desc, &tail, 10);
+		if (errno || tail == time_desc || *tail != '\0')
 			goto error;
 	} else if (*tail != '\0') {
 		goto error;