s3:lib: Use memcpy() in escape_ldap_string()

../source3/lib/ldap_escape.c: In function ‘escape_ldap_string’:
../source3/lib/ldap_escape.c:79:4: error: ‘strncpy’ output truncated
    before terminating nul copying 3 bytes from a string of the same length
[-Werror=stringop-truncation]
    strncpy (p, sub, 3);
    ^~~~~~~~~~~~~~~~~~~

We concatenat and do not care about NUL-termination till the loop has
finished.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13437

Signed-off-by: Andreas Schneider <[email protected]>
Reviewed-by: Guenther Deschner <[email protected]>

source3/lib/ldap_escape.c

@@ -76,7 +76,7 @@ char *escape_ldap_string(TALLOC_CTX *mem_ctx, const char *s)
 			output = tmp;
 
 			p = &output[i];
-			strncpy (p, sub, 3);
+			memcpy(p, sub, 3);
 			p += 3;
 			i += 3;