Fix error C4703 on VS 2019 build

[ghost]

The following errors occur when building the library in Visual Studio 2019 (cl):

expand.c(410): error C4703: potentially uninitialized local pointer variable 'm_inf' used
expand.c(539): error C4703: potentially uninitialized local pointer variable 'm_inf' used
expand.c(1909): error C4703: potentially uninitialized local pointer variable 'loc' used
expand.c(1909): error C4703: potentially uninitialized local pointer variable 'locs' used
expand.c(1626): error C4703: potentially uninitialized local pointer variable 'inner' used
expand.c(1234): error C4703: potentially uninitialized local pointer variable 'loc_tab' used

Initializing the pointers with NULL resolves the error.

[pepone]

Thanks for the fix Nik