Add in a missing data_reader check when creating subscription. (#697)

The end stanza of create_datareader() is supposed to be
attempting to create a datareader with the underlying Fast-DDS
library.  If creation of the datareader returns a valid
pointer, we've succeeded, and if it returns a nullptr, it
has failed.

However, there were two separate problems of the logic
checking for these conditions:

1. It was checking the datareader pointer-to-a-pointer,
which should always be non-null.  What it really meant to
check was the datareader pointer (dereferenced).
2. There is a fallback mechanism for when unique network
flow endpoints were optionally required.  The problem with
that is that when using the fallback, we never check again
to make sure the fallback was successful.  Therefore, if
we failed for another reason (like security), we would
not discover it until a crash later on.

This commit fixes both of these issues.

Signed-off-by: Chris Lalancette <[email protected]>

rmw_fastrtps_shared_cpp/src/utils.cpp

@@ -162,7 +162,7 @@ create_datareader(
     updated_qos,
     listener,
     eprosima::fastdds::dds::StatusMask::subscription_matched());
-  if (!data_reader &&
+  if (!(*data_reader) &&
     (RMW_UNIQUE_NETWORK_FLOW_ENDPOINTS_OPTIONALLY_REQUIRED ==
     subscription_options->require_unique_network_flow_endpoints))
   {
@@ -172,6 +172,11 @@ create_datareader(
       listener,
       eprosima::fastdds::dds::StatusMask::subscription_matched());
   }
+
+  if (!(*data_reader)) {
+    return false;
+  }
+
   return true;
 }