add some asserts to help static analyzers

From: Stefan Bühler <stbuehler@web.de>

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2957 152afb58-edef-0310-8abb-c4023f1b3aa9

src/log.c

@@ -362,6 +362,7 @@ static void log_write(server *srv, buffer *b) {
 	case ERRORLOG_FILE:
 	case ERRORLOG_FD:
 		buffer_append_string_len(b, CONST_STR_LEN("\n"));
+		force_assert(b->used > 0);
 		write(srv->errorlog_fd, b->ptr, b->used - 1);
 		break;
 	case ERRORLOG_SYSLOG:

src/mod_accesslog.c

@@ -915,6 +915,7 @@ REQUESTDONE_FUNC(log_access_write) {
 			}
 #endif
 		} else if (p->conf.log_access_fd != -1) {
+			force_assert(b->used > 0);
 			write(p->conf.log_access_fd, b->ptr, b->used - 1);
 		}
 		buffer_reset(b);

src/mod_secure_download.c

@@ -255,6 +255,7 @@ URIHANDLER_FUNC(mod_secdownload_uri_handler) {
 	buffer_copy_string_buffer(p->md5, p->conf.secret);
 	buffer_append_string(p->md5, rel_uri);
 	buffer_append_string_len(p->md5, ts_str, 8);
+	force_assert(p->md5->used > 0);
 
 	li_MD5_Init(&Md5Ctx);
 	li_MD5_Update(&Md5Ctx, (unsigned char *)p->md5->ptr, p->md5->used - 1);

src/server.c

@@ -1001,6 +1001,7 @@ int main (int argc, char **argv) {
 	if (pid_fd != -1) {
 		buffer_copy_long(srv->tmp_buf, getpid());
 		buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN("\n"));
+		force_assert(srv->tmp_buf->used > 0);
 		write(pid_fd, srv->tmp_buf->ptr, srv->tmp_buf->used - 1);
 		close(pid_fd);
 		pid_fd = -1;