Fix warnings about passing uninitialized buffers into functions

Most of these buffers were never actually inspected, but it's still
bad style.

src/common/buffers.c

@@ -907,6 +907,8 @@ buf_peek_startswith(const buf_t *buf, const char *cmd)
 {
   char tmp[PEEK_BUF_STARTSWITH_MAX];
   size_t clen = strlen(cmd);
+  if (clen == 0)
+    return 1;
   if (BUG(clen > sizeof(tmp)))
     return 0;
   if (buf->datalen < clen)

src/common/compat.c

@@ -2580,6 +2580,7 @@ tor_inet_pton(int af, const char *src, void *dst)
     int gapPos = -1, i, setWords=0;
     const char *dot = strchr(src, '.');
     const char *eow; /* end of words. */
+    memset(words, 0xf8, sizeof(words));
     if (dot == src)
       return 0;
     else if (!dot)