bin/bfs_tools: Fix array index is out of bounds

If length == BPLUSTREE_MAX_KEY_LENGTH at line 237,
buffer[] index may be out of bounds at line 245.
Pointed out by cppcheck.

Change-Id: Ib86abeaa72526b327af85ca9a26b050834f5a2c9
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3501
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

src/bin/bfs_tools/lib/dump.cpp

@@ -240,7 +240,7 @@ dump_bplustree_node(const bplustree_node* node, const bplustree_header* header,
 			break;
 		}
 
-		char buffer[256];
+		char buffer[BPLUSTREE_MAX_KEY_LENGTH + 1];
 		memcpy(buffer, key, length);
 		buffer[length] = '\0';