proxyclient: avoid to generate tokens with \0

src/dht_proxy_client.cpp

@@ -98,7 +98,7 @@ getRandomSessionId(size_t length = 8) {
     static constexpr const char chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&()*+,./:;<=>?@[]^_`{|}~";
     std::string str(length, 0);
     crypto::random_device rdev;
-    std::uniform_int_distribution<> dist(0, (sizeof(chars)/sizeof(char)) - 1);
+    std::uniform_int_distribution<> dist(0, (sizeof(chars)/sizeof(char)) - 2);
     std::generate_n( str.begin(), length, [&]{ return chars[dist(rdev)]; } );
     return str;
 }