Return from addrbook_load if a file is empty.

src/addrbook.c

@@ -46,9 +46,12 @@ int addrbook_load(addrbook_t *ab, FILE *in) {
     char *line = NULL;
     size_t line_len = 0;
     size_t lines = 0;
-
-    while (getline(&line, &line_len, in) != -1)
+    while (getline(&line, &line_len, in) != -1) {
         ++lines;
+    }
+
+    if (lines == 0)
+        return -1;
 
     if (ab->entries != NULL)
         free(ab->entries);