Fix crash caused by NULL lookup when reporting IP address of failed

libpq connection, per report from Magnus.  This happens only on GIT
master and only on Win32 because that is the platform where "" maps to
an IP address (localhost).

src/interfaces/libpq/fe-connect.c

@@ -1031,7 +1031,8 @@ connectFailureMessage(PGconn *conn, int errorno)
 			strcpy(host_addr, "???");
 
 		display_host_addr = (conn->pghostaddr == NULL) &&
-			(strcmp(conn->pghost, host_addr) != 0);
+							(conn->pghost != NULL) &&
+							(strcmp(conn->pghost, host_addr) != 0);
 
 		appendPQExpBuffer(&conn->errorMessage,
 						  libpq_gettext("could not connect to server: %s\n"