Fix sql.php behavior on error

Fix sql.php behavior on error

When an erroneous query is entered into sql.php, it doesn't clear its
line buffer, so the intended next query (often fixing a typo in the
original) winds up concatenated onto the erroneous query. Usually
leading to another error, which repeats the process.

The solution is simple enough: clear the line buffer unconditionally,
not only when no exception is caught.

Change-Id: Ia78e2df8b9c6698c0a225bfb3135274ed8da5303