stack_size miscalculations / locals() dict corruptions

[pmp-p]

only for certain patterns like :

def f(r=1,g=2):
    print(r,g)

def f(r=1,g=2,b=3):
    print(r,g,b)

etc ...

will lead the pre-emptible version of func_bc_call() to crash either with exhausting pystack with a huge size request ( DECODE_CODESTATE_SIZE ) for mp_pystack_alloc() or by trashing the locals() dict when function body is executed ( ie symbols r,g,b won't be solved).