BUG: fix small issues found with cppcheck

uninitialized use in _strided_to_strided_one_to_n_with_finish
wrong error NULL checks in PyArray_MapIterNew and einsum_sub_op_from_str
double free and memleak in umath_linalg.c.src init_@lapack_func@
Merge pull request #3964 from charris/backport-1.7-3832

backport-1.7-3832