assert non-NULL ptrs before calling mem funcs

The definitions of memcpy(), memmove(), and memset() state that
the behaviour is undefined if any of the pointer arguments are
NULL, and some compilers are known to make use of this to
optimise away existing NULL checks in the source.

Change-Id: I489bc256e3eac7ff41d91becb0b43aba73dbb3f9
Link: https://www.imperialviolet.org/2016/06/26/nonnull.html

lib/krb5/pac.c

@@ -35,6 +35,7 @@
 
 #include <heimbasepriv.h>
 #include <wind.h>
+#include <assert.h>
 
 struct PAC_INFO_BUFFER {
     uint32_t type;
@@ -382,6 +383,8 @@ krb5_pac_add_buffer(krb5_context context, krb5_pac p,
     size_t len, offset, header_end, old_end;
     uint32_t i;
 
+    assert(data->length > 0 && data->data != NULL);
+
     len = p->pac->numbuffers;
 
     ptr = realloc(p->pac,
@@ -1101,7 +1104,7 @@ build_logon_name(krb5_context context,
 	    krb5_set_error_message(context, ret, "Principal %s is not valid UTF-8", s);
 	    free(s);
 	    return ret;
-	} else 
+	} else
 	    free(s);
 
 	s2_len = (ucs2_len + 1) * 2;