rand: add a clang-analyzer work-around

scan-build would warn on a potential access of an uninitialized
buffer. I deem it a false positive and had to add this somewhat ugly
work-around to silence it.

lib/rand.c

@@ -157,6 +157,12 @@ CURLcode Curl_rand_hex(struct Curl_easy *data, unsigned char *rnd,
   unsigned char *bufp = buffer;
   DEBUGASSERT(num > 1);
 
+#ifdef __clang_analyzer__
+  /* This silences a scan-build warning about accesssing this buffer with
+     uninitialized memory. */
+  memset(buffer, 0, sizeof(buffer));
+#endif
+
   if((num/2 >= sizeof(buffer)) || !(num&1))
     /* make sure it fits in the local buffer and that it is an odd number! */
     return CURLE_BAD_FUNCTION_ARGUMENT;