Upgrade unbound library

These files were pulled from the 1.6.3 release tarball.

This new version builds against OpenSSL version 1.1 which will be
the default in the new Debian Stable which is due to be released
RealSoonNow (tm).

external/unbound/sldns/sbuffer.c

@@ -33,6 +33,7 @@ sldns_buffer_new(size_t capacity)
 	buffer->_position = 0;
 	buffer->_limit = buffer->_capacity = capacity;
 	buffer->_fixed = 0;
+	buffer->_vfixed = 0;
 	buffer->_status_err = 0;
 	
 	sldns_buffer_invariant(buffer);
@@ -48,6 +49,7 @@ sldns_buffer_new_frm_data(sldns_buffer *buffer, void *data, size_t size)
 	buffer->_position = 0; 
 	buffer->_limit = buffer->_capacity = size;
 	buffer->_fixed = 0;
+	buffer->_vfixed = 0;
 	buffer->_data = malloc(size);
 	if(!buffer->_data) {
 		buffer->_status_err = 1;
@@ -66,6 +68,17 @@ sldns_buffer_init_frm_data(sldns_buffer *buffer, void *data, size_t size)
 	buffer->_data = data;
 	buffer->_capacity = buffer->_limit = size;
 	buffer->_fixed = 1;
+	buffer->_vfixed = 0;
+}
+
+void
+sldns_buffer_init_vfixed_frm_data(sldns_buffer *buffer, void *data, size_t size)
+{
+	memset(buffer, 0, sizeof(*buffer));
+	buffer->_data = data;
+	buffer->_capacity = buffer->_limit = size;
+	buffer->_fixed = 1;
+	buffer->_vfixed = 1;
 }
 
 int
@@ -74,7 +87,7 @@ sldns_buffer_set_capacity(sldns_buffer *buffer, size_t capacity)
 	void *data;
 	
 	sldns_buffer_invariant(buffer);
-	assert(buffer->_position <= capacity);
+	assert(buffer->_position <= capacity && !buffer->_fixed);
 
 	data = (uint8_t *) realloc(buffer->_data, capacity);
 	if (!data) {
@@ -126,7 +139,7 @@ sldns_buffer_printf(sldns_buffer *buffer, const char *format, ...)
 		if (written == -1) {
 			buffer->_status_err = 1;
 			return -1;
-		} else if ((size_t) written >= remaining) {
+		} else if (!buffer->_vfixed && (size_t) written >= remaining) {
 			if (!sldns_buffer_reserve(buffer, (size_t) written + 1)) {
 				buffer->_status_err = 1;
 				return -1;