Fix uni2asc() so it can properly convert zero length

unicode strings. Certain PKCS#12 files contain these
in BMPStrings and it used to crash on them.

CHANGES

@@ -3,6 +3,10 @@
 
  Changes between 0.9.6 and 0.9.7  [xx XXX 2000]
 
+  *) Fix to uni2asc() to cope with zero length Unicode strings.
+     These are present in some PKCS#12 files.
+     [Steve Henson]
+
   *) Finish off removing the remaining LHASH function pointer casts.
      There should no longer be any prototype-casting required when using
      the LHASH abstraction, and any casts that remain are "bugs". See

crypto/pkcs12/p12_utl.c

@@ -83,7 +83,7 @@ char *uni2asc (unsigned char *uni, int unilen)
 	char *asctmp;
 	asclen = unilen / 2;
 	/* If no terminating zero allow for one */
-	if (uni[unilen - 1]) asclen++;
+	if (!unilen || uni[unilen - 1]) asclen++;
 	uni++;
 	if (!(asctmp = OPENSSL_malloc (asclen))) return NULL;
 	for (i = 0; i < unilen; i+=2) asctmp[i>>1] = uni[i];