After handling (or not handling) a \ command, continue with reading the next input line, don't ever send the \ line to the server.
After handling (or not handling) a \ command, continue with reading
the next input line, don't ever send the \ line to the server.

When an empty line is sent from the server, handle it as any other
line.  This fixes a bug introduced in revision 1.49 which caused
MonetDB4/src/mapi/Tests/monet_BATs to fail.

Don't attempt reading another line after mapi_fetch_line returned
NULL.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb