msrledec: move output pointer test up

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
msrledec: move loop into switch

speeds up code and allows more simplifications

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
msrledec: merge switches

More speedup and fixes 'may be used uninitialized in this function' warnings

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>