A fix and a test case for Bug#15217 "Using a SP cursor on a table created
with PREPARE fails with weird error". More generally, re-executing a stored procedure with a complex SP cursor query could lead to a crash. The cause of the problem was that SP cursor queries were not optimized properly at first execution: their parse tree belongs to sp_instr_cpush, not sp_instr_copen, and thus the tree was tagged "EXECUTED" when the cursor was declared, not when it was opened. This led to loss of optimization transformations performed at first execution, as sp_instr_copen saw that the query is already "EXECUTED" and therefore either not ran first-execution related blocks or wrongly rolled back the transformations caused by first-execution code. The fix is to update the state of the parsed tree only when the tree is executed, as opposed to when the instruction containing the tree is executed. Assignment if i->state is moved to reset_lex_and_exec_core.
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