Set errno for expand function of the string list.

src/std/c_string.c

@@ -100,6 +100,7 @@ int c_strlist_add(c_strlist_t *strlist, const char *string) {
     }
     strlist->count++;
   } else {
+    errno = ENOBUFS;
     return -1;
   }
 

src/std/c_string.h

@@ -92,7 +92,8 @@ c_strlist_t *c_strlist_expand(c_strlist_t *strlist, size_t size);
  * @param strlist  Stringlist to add the string.
  * @param string   String to add.
  *
- * @return  0 on success, less than 0 if an error occured.
+ * @return  0 on success, less than 0 and errno set if an error occured.
+ *          ENOBUFS if the list is full.
  */
 int c_strlist_add(c_strlist_t *strlist, const char *string);