An error occuring in the execution of a stored procedure, called
from do_select is masked, since the error condition is not
propagated back to the caller (join->conds->val_int() returns
a result value, and not an error code)
                  
An explicit check was added to see if the thd error code has been
set, and if so, the loop status is set to the error state.

Backport from 6.0-codebase (revid: 2617.68.31)