fix header-only file crash, fixes #67

diff --git a/src/markdown.c b/src/markdown.c
index 05c77be..8471724 100644 (file)
--- a/src/markdown.c
+++ b/src/markdown.c
@@ -81,6 +81,8 @@ void free_deck(deck_t *deck) {
     while (slide) {
         free_line(slide->line);
         next = slide->next;
+        if (slide == NULL)
+            return;
         free(slide);
         slide = next;
     }