compare_string_array: code shrink

Code shrink and prevention of possible out of bounds access.

function                                             old     new   delta
nth_string                                            36      26     -10
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-10)             Total: -10 bytes
   text	   data	    bss	    dec	    hex	filename
 981342	  16915	   1872	1000129	  f42c1	busybox_old
 981332	  16915	   1872	1000119	  f42b7	busybox_unstripped

Signed-off-by: Martin Lewis <martin.lewis.x84@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/libbb/compare_string_array.c b/libbb/compare_string_array.c
index 01a9df0e2..a06e57d3d 100644
--- a/libbb/compare_string_array.c
+++ b/libbb/compare_string_array.c
@@ -117,8 +117,11 @@ int FAST_FUNC index_in_substrings(const char *strings, const char *key)
 const char* FAST_FUNC nth_string(const char *strings, int n)
 {
         while (n) {
-                n--;
-                strings += strlen(strings) + 1;
+                if (*strings++ == '\0') {
+                        if (*strings == '\0') /* reached end of strings */
+                                break;
+                        n--;
+                }
         }
         return strings;
 }