[C++] Incorrect variadic buffer count in IPC can easily blow up memory

[pitrou]

Describe the bug, including details regarding any error messages, version, and platform.

Reported by OSS-Fuzz at https://issues.oss-fuzz.com/issues/476180608, and separately to the Arrow PMC.

Component(s)

C++

[pitrou]

Issue resolved by pull request 48901
#48901