Fix some random crashes when using argument buffers

Fixes an issue with BitArray enumeration, where it
could iterate over bit indices that weren't set

This would cause issues in descriptor set allocation,
when argument buffers are enabled, where it could
select a set index from the pool that isn't freed,
and try to create a new set on top of the exiting one

MoltenVK/MoltenVK/Utility/MVKBitArray.h

@@ -155,7 +155,7 @@ class MVKBitArray {
 	bool enumerateEnabledBits(bool shouldClear, std::function<bool(size_t bitIndex)> func) {
 		for (size_t bitIdx = getIndexOfFirstSetBit(shouldClear);
 			 bitIdx < _bitCount;
-			 getIndexOfFirstSetBit(++bitIdx, shouldClear)) {
+			 bitIdx = getIndexOfFirstSetBit(++bitIdx, shouldClear)) {
 
 			if ( !func(bitIdx) ) { return false; }
 		}