[LAA] Check HasSameSize before couldPreventStoreLoadForward.

After 96452676, TypeByteSize is 0 if both access do not have the same
size (i.e. HasSameSize will be false). This can cause an infinite loop
in couldPreventStoreLoadForward, if HasSameSize is not checked first.

So check HasSameSize first instead of after
couldPreventStoreLoadForward. Checking HasSameSize first is also
cheaper.