rpki-client(8): properly zero terminate pretty printed key

[Martin Vahlensieck]

Hi

It seems the pretty printed key is zero terminated only if the size
of hex stays the same or increases between calls.  This diff fixes
it, so it is always properly terminated.  While here, also drop
*hex != '\0' from the if inside the loop, as it is checked directly
above in the loop condition and constify the argument, as it is not
modified.

Best,

Martin

Index: print.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/print.c,v
retrieving revision 1.5
diff -u -p -r1.5 print.c
--- print.c     10 Feb 2022 17:33:28 -0000      1.5
+++ print.c     17 Mar 2022 17:46:01 -0000
@@ -28,19 +28,21 @@
 #include "extern.h"
 
 static const char *
-pretty_key_id(char *hex)
+pretty_key_id(const char *hex)
 {
        static char buf[128];   /* bigger than SHA_DIGEST_LENGTH * 3 */
        size_t i;
 
        for (i = 0; i < sizeof(buf) && *hex != '\0'; i++) {
-               if  (i % 3 == 2 && *hex != '\0')
+               if  (i % 3 == 2)
                        buf[i] = ':';
                else
                        buf[i] = *hex++;
        }
        if (i == sizeof(buf))
                memcpy(buf + sizeof(buf) - 4, "...", 4);
+       else
+               buf[i] = '\0';
        return buf;
 }