[cppcheck] resource leaks in btree

cppcheck detects two leaks which can occur in ./src/3rdparty/btree/src/btree.cpp .

The error report is:

[./src/3rdparty/btree/src/btree.cpp:4102]: (error) Resource leak: fd
[./src/3rdparty/btree/src/btree.cpp:4144]: (error) Memory leak: p

Both leaks are in the btree_dump_page_from_file function.
Firstly, a file is opened and never closed, leaking a file descriptor.
Secondly, a calloc() is performed and the memory is not freed if an error occurs reading from the file.