Fix: zero out URL parsing array before use and ensure proper error reporting

Fix: zero out URL parsing array before use and ensure proper error reporting

The remain[2] array is being used uninitialized when such URI is used:
`net://localhost:1234`.
The following line (142) will return 1:
  `ret = sscanf(remain[0], ":%d%s", &ctx->port, remain[1]);`
because `sscanf` won't match on the string (%s) delimiter.
This will leave `remain[2]` uninitialized.

This potentially uninitialized array is being used further down the function.

As a fix, we zero out the array at initialization time to prevent the
`strlen(remain[2])` call from using uninitialized memory.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>