An empty file does not have a positive number of lines.

Make sure that the number of lines read is non-zero before in order to
avoid dumping core.

Reported by:	Wojciech A. Koszek
Pointy hat to:	cperciva

usr.sbin/portsnap/make_index/make_index.c

@@ -411,6 +411,7 @@ printport(PORT * p)
 /*
  * Algorithm:
  * 1. Suck in all the data, splitting into fields.
+ * 1a. If there are no ports, there is no INDEX.
  * 2. Sort the ports according to port directory.
  * 3. Using a binary search, translate each dependency from a
  * port directory name into a pointer to a port.
@@ -469,6 +470,12 @@ main(int argc, char *argv[])
 	if (fclose(f) != 0)
 		err(1, "fclose(%s)", argv[1]);
 
+	/*
+	 * 1a. If there are no ports, there is no INDEX.
+	 */
+	if (pplen == 0)
+		return 0;
+
 	/*
 	 * 2. Sort the ports according to port directory.
 	 */