Fix potential free of null pointer in stringlist_delete

CHANGES.md

@@ -7,6 +7,7 @@ Bug Fixes
     - Fix writing and reading of string columns with length
       1 vectors in numpy 2.
     - Fix building against NumPy 2.3.0.
+    - Fix potential free of null pointer in stringlist_delete
 
 version 1.2.5
 -------------

fitsio/fitsio_pywrap.c

@@ -305,10 +305,12 @@ static struct stringlist* stringlist_delete(struct stringlist* slist) {
         size_t i=0;
         if (slist->data != NULL) {
             for (i=0; i < slist->size; i++) {
-                free(slist->data[i]);
+                if (slist->data[i] != NULL) {
+                    free(slist->data[i]);
+                }
             }
+            free(slist->data);
         }
-        free(slist->data);
         free(slist);
     }
     return NULL;