Fix two bugs found by a new clang warning I'm currently testing:

base/md5.cc

Index: base/md5.cc
diff --git a/base/md5.cc b/base/md5.cc
index f85cf4390d954663662bb65d1637220d6bbb6d4a..fdda2a499c06dea8f6ed5bb023db4eb72af08e43 100644
--- a/base/md5.cc
+++ b/base/md5.cc
@@ -247,7 +247,7 @@ void MD5Final(MD5Digest* digest, MD5Context *pCtx){
         MD5Transform(ctx->buf, (uint32 *)ctx->in);
         byteReverse((unsigned char *)ctx->buf, 4);
         memcpy(digest->a, ctx->buf, 16);
-        memset(ctx, 0, sizeof(ctx));    /* In case it's sensitive */
+        memset(ctx, 0, sizeof(*ctx));    /* In case it's sensitive */
 }
 
 std::string MD5DigestToBase16(const MD5Digest& digest){