Patch: Don't clear out the full buffer when constructing a log message

[markdoliner]

The log_write() function gets called a lot. It takes some input parameters and puts them into a buffer, then prints the buffer. Before it puts the parameters into the buffer it memset's the entire thing to 0. It's probably more efficient to NOT memset it and instead just null terminate the message after the call to vsnprintf() or snprintf().

[smoku]

(In [431]) Don't clear out the full buffer when constructing a log message. Fixes #162