FR: add jassert to AudioBuffer (Type* const* dataToReferTo

AudioBuffer has a handy constructor to create a buffer using a preallocated part of memory, normally this won’t allocate any extra memory on heap (because it uses a preallocated channel space), so it can be used on the stack

(for very specific reasons i need to use a AudioBuffer instead a AudioBlock) *

it would be nice if this could be added to the constructor to ensure that no extra memory will be allocated

jassert(numChannelsToUse < (int)numElementsInArray(preallocatedChannelSpace));

alternatively it would be great if there is a static access to the size of preallocatedChannelSpace-array.