A failing transformation is indicated by marking the parse
tree as broken. But this mark was not read by the code that
executes the SET command in stored procedures. In this case,
transformations such as outer-to-inner join conversion are
carried out as part of evaluating a subquery when it is
the rvalue, as opposed to doing it during normal
preparation, i.e. in select_lex::prepare().

Fixed by moving the check from mysql_execute_command() to
reinit_stmt_before_use(), where the check can be reused for
all code paths that must deal with a possibly broken parse
tree, i.e. prepared statements and stored procedured.