Honor unlimited negotiated frame_max when capping inbound message size (backport #2015) - #2016
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AMQConnection derived the inbound frame payload limit with Math.min(maxInboundMessageBodySize, frameMax), but a negotiated frame_max of 0 means "no limit" (see negotiatedMaxValue and AMQCommand#transmit), not a literal zero. Math.min silently turned that into a limit of 0, which Utils.framePayloadLimit then treated as "no limit" again, so the configured message body cap was discarded in favor of an effectively unbounded frame size. A frame_max of 0 is reachable via the client's own default (requestedFrameMax is 0 unless overridden) whenever the broker also negotiates 0, so maxInboundMessageBodySize could end up unenforced without any non-default client configuration. Add Utils.inboundFrameMax to compute the effective limit correctly, with a UtilsTest covering the arithmetic directly and two InboundFrameMax cases exercising it end to end against a fake broker that negotiates frame_max=0. (cherry picked from commit 6d7c2bf)
connection.tune's frame_max is parsed via a signed 32-bit read, so a broker can send a value with the high bit set and have it come back negative once negotiated. Unlike negotiatedChannelMax and negotiatedHeartbeat, the negotiated frameMax was never validated afterwards. A negative frameMax reaching Utils.inboundFrameMax defeats the Math.min against maxInboundMessageBodySize, since the negative value is always the smaller one, then trips the same "frame_max <= 0 means no limit" fallback in Utils.framePayloadLimit that frame_max=0 relies on for its legitimate meaning, reintroducing the size-cap bypass without a broker ever needing to negotiate a literal 0. A non-default, positive requestedFrameMax is also enough to reach this on its own, with an otherwise honest broker, since negotiatedMaxValue only launders a negative value back to 0 when one side's value is exactly 0. Reject the negotiated frame max outright when negative, the same way the sibling channel max and heartbeat checks already do. (cherry picked from commit 89ed7ea)
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This is an automatic backport of pull request #2015 done by [Mergify](https://mergify.com).