Handle a lack of login/password information without segfaulting.

If datacopy is called incorrectly with, e.g., /dev/null on stdin, it won't
get any database login/password information.  We should print an error
message and exit instead of throwing a segfault trying to copy a null
pointer.

Rather than exiting immediately, though, just try to connect to the
databases without a username/password, because hey, you never know.

Bug-Debian: http://bugs.debian.org/715785

src/apps/datacopy.c

@@ -455,8 +455,10 @@ login_to_databases(BCPPARAMDATA * pdata, DBPROCESS ** dbsrc, DBPROCESS ** dbdest
 
 	slogin = dblogin();
 
-	DBSETLUSER(slogin, pdata->suser);
-	DBSETLPWD(slogin, pdata->spass);
+	if (pdata->suser)
+		DBSETLUSER(slogin, pdata->suser);
+	if (pdata->spass)
+		DBSETLPWD(slogin, pdata->spass);
 	DBSETLAPP(slogin, "Migrate Data");
 
 	/* if packet size specified, set in login record */
@@ -481,8 +483,10 @@ login_to_databases(BCPPARAMDATA * pdata, DBPROCESS ** dbsrc, DBPROCESS ** dbdest
 
 	dlogin = dblogin();
 
-	DBSETLUSER(dlogin, pdata->duser);
-	DBSETLPWD(dlogin, pdata->dpass);
+	if (pdata->duser)
+		DBSETLUSER(dlogin, pdata->duser);
+	if (pdata->dpass)
+		DBSETLPWD(dlogin, pdata->dpass);
 	DBSETLAPP(dlogin, "Migrate Data");
 
 	/* Enable bulk copy for this connection. */