Very minor issues found with statical analysis.

The Clang Static Analyzer uncovered those issues:

- The variable "changed" in handlers.c is written to, but it's
  never read since that specific write, so the write is not
  necessary.

- In util.c, "tail" may be NULL. In that case, we shouldn't pass
  it to strlen because strlen's behavior is not defined when s is
  NULL.

- In util.c, "write_index" is incremented twice. It's never used
  anymore after being incremented once, so the second increment is
  not necessary.

src/handlers.c

@@ -751,7 +751,6 @@ int handle_normal_hints(void *data, xcb_connection_t *conn, uint8_t state, xcb_w
         con->base_height = base_height;
         DLOG("client's base_height changed to %d\n", base_height);
         DLOG("client's base_width changed to %d\n", base_width);
-        changed = true;
     }
 
     /* If no aspect ratio was set or if it was invalid, we ignore the hints */