static-delta: guard bspatch against integer truncation on 32-bit

static-delta: guard bspatch against integer truncation on 32-bit

On 32-bit systems (sizeof(gsize)==4), the attacker-controlled
content_size (a guint64) is silently truncated when passed to
g_malloc0(), which takes gsize.  Meanwhile bspatch() receives the
full 64-bit value as int64_t newsize and writes according to it,
producing a heap buffer overflow.

Add an explicit check that content_size fits in both gsize and int64_t
before the allocation.  Use separate typed locals (alloc_size, newsize)
to make the truncation-free intent clear and pass newsize to bspatch().

Addresses: RHEL-189207
CWE-680, CWE-122, CWE-190