Security fix for CERT issue VU#922681

This patch addresses three possible buffer overflows in function
unique_service_name(). The three issues have the folowing CVE
numbers:

CVE-2012-5958 Issue #2: Stack buffer overflow of Tempbuf
CVE-2012-5959 Issue #4: Stack buffer overflow of Event->UDN
CVE-2012-5960 Issue #8: Stack buffer overflow of Event->UDN

Notice that the following issues have already been dealt by previous
work:

CVE-2012-5961 Issue #1: Stack buffer overflow of Evt->UDN
CVE-2012-5962 Issue #3: Stack buffer overflow of Evt->DeviceType
CVE-2012-5963 Issue #5: Stack buffer overflow of Event->UDN
CVE-2012-5964 Issue #6: Stack buffer overflow of Event->DeviceType
CVE-2012-5965 Issue #7: Stack buffer overflow of Event->DeviceType