`tt_var_load_item_variation_store` fills out a `GX_ItemVarStore`. While it
may return an error, the item store must be left in a consistent state so
that any use or destruction of the item store can properly use or free the
data in it. Before this change the counts from the font data were read
directly into the item store before the actual allocation of the arrays to
which they referred. There exist many opportunities between the time the
counts are read and the arrays are allocated to return early due to invalid
data. When this happened the item store claimed to have entires it actually
did not, leading to crashes later when it was used.
Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=54449
* src/truetype/ttgxvar.c (tt_var_load_item_variation_store): Read the counts
into local variables and store them in the item store only after the related
arrays are actually created on the item store.