[hackers] [sbase] tr: set2 must be set in some cases || Hiltjo Posthuma

[git]

commit 14c5ab48d504c35fd0f4d196ca11e6f9a6aaff33
Author: Hiltjo Posthuma <hil...@codemadness.org>
Date:   Sat Jan 10 19:08:54 2015 +0100

    tr: set2 must be set in some cases
    
    echo abc | tr 'a' '' would crash because of:
    
        m--;
        r = set2[m].start + (off1 - off2) / set2[m].quant;
    
    if set2ranges > 0 it's fine.

diff --git a/tr.c b/tr.c
index 03a7c2a..973c73b 100644
--- a/tr.c
+++ b/tr.c
@@ -196,6 +196,8 @@ main(int argc, char *argv[])
        set1ranges = makeset(argv[0], &set1);
        if (argc == 2)
                set2ranges = makeset(argv[1], &set2);
+       if (!dflag && !set2ranges)
+               eprintf("set2 must be non-empty\n");
 read:
        if (!readrune("<stdin>", stdin, &r))
                return 0;