Client: fix interpretation of zero timeout value in NetProviders

As per the `Connector::wait*` API documentation, the zero timeout value
means an infinite timeout:
> `timeout = 0` means the method is polling the future until the response
> is ready. [1]

The zero timeout value is completely misinterpreted in the
`LibevNetProvider` — a timeout timer should only be created if the timeout
is non-zero.

The zero timeout value is oddly interpreted in the `LibevNetProvider` — the
corresponding infinite timeout value in the epoll API is `-1`.

Closes #61

1. https://www.tarantool.io/en/doc/latest/book/connectors/cxx/tntcxx_api/#_CPPv44waitR10ConnectionI6BUFFER11NetProviderE5rid_ti

src/Client/EpollNetProvider.hpp

@@ -64,7 +64,7 @@ class EpollNetProvider {
 	int wait(int timeout);
 
 private:
-	static constexpr size_t DEFAULT_TIMEOUT = 100;
+	static constexpr int TIMEOUT_INFINITY = -1;
 	static constexpr size_t EPOLL_EVENTS_MAX = 128;
 
 	//return 0 if all data from buffer was processed (sent or read);
@@ -261,7 +261,7 @@ EpollNetProvider<BUFFER, Stream>::wait(int timeout)
 {
 	assert(timeout >= 0);
 	if (timeout == 0)
-		timeout = DEFAULT_TIMEOUT;
+		timeout = TIMEOUT_INFINITY;
 	LOG_DEBUG("Network engine wait for ", timeout, " milliseconds");
 	/* Send pending requests. */
 	for (auto conn = m_Connector.m_ReadyToSend.begin();

src/Client/LibevNetProvider.hpp

@@ -361,8 +361,10 @@ int
 LibevNetProvider<BUFFER, Stream>::wait(int timeout)
 {
 	assert(timeout >= 0);
-	ev_timer_init(&m_TimeoutWatcher, &timeout_cb, timeout / MILLISECONDS, 0 /* repeat */);
-	ev_timer_start(m_Loop, &m_TimeoutWatcher);
+	if (timeout > 0) {
+		ev_timer_init(&m_TimeoutWatcher, &timeout_cb, timeout / MILLISECONDS, 0 /* repeat */);
+		ev_timer_start(m_Loop, &m_TimeoutWatcher);
+	}
 	/* Queue pending connections to be send. */
 	for (auto conn = m_Connector.m_ReadyToSend.begin();
 	     conn != m_Connector.m_ReadyToSend.end();) {