radix_tree: fix internal find

Fix comparison between n->byte and key.size(). When using pmem::obj::string
or inline_string the behavior was ok (since we always have null terminator
at the end), but we technically access out-of-range memory which can cause
asserts in string_view operator[].

Author: igchor

include/libpmemobj++/experimental/radix_tree.hpp

@@ -1744,7 +1744,7 @@ radix_tree<Key, Value, BytesView>::internal_find(const K &k) const
 	while (n && !n.is_leaf()) {
 		if (path_length_equal(key.size(), n))
 			n = n->embedded_entry;
-		else if (n->byte > key.size())
+		else if (n->byte >= key.size())
 			return nullptr;
 		else
 			n = n->child[slice_index(key[n->byte], n->bit)];