rtmpdump: multiple vulnerabilities

The following is a list of vulnerabilities fixed:

• Additional decode input size checks
• Ignore zero-length packets
• Potential integer overflow in RTMPPacket_Alloc().
• Obsolete RTMPPacket_Free() call left over from original C++ to C rewrite
• AMFProp_GetObject must make sure the prop is actually an object

A remote attacker could entice a user to open a specially crafted media flash file using RTMPDump. This could possibly result in the execution of arbitrary code with the privileges of the process or a Denial of Service condition.