Rewinder - when reallocating buffer, make sure we have released all references to the old buffer first to free up memory for the new buffer.

BizHawk.Client.Common/rewind/Rewinder.cs

@@ -235,12 +235,14 @@ namespace BizHawk.Client.Common
 				// if we have an appropriate buffer free, return it
 				if (_rewindBufferBacking != null)
 				{
-					var buf = _rewindBufferBacking;
-					_rewindBufferBacking = null;
-					if (buf.LongLength == size)
+					if (_rewindBufferBacking.LongLength == size)
 					{
+						var buf = _rewindBufferBacking;
+						_rewindBufferBacking = null;
 						return buf;
 					}
+
+					_rewindBufferBacking = null;
 				}
 
 				// otherwise, allocate it

BizHawk.Client.Common/rewind/StreamBlobDatabase.cs

@@ -65,6 +65,7 @@ namespace BizHawk.Client.Common
 			{
 				long capacity = 0;
 				_mBufferManage(_mAllocatedBuffer, ref capacity, false);
+				_mAllocatedBuffer = null;
 			}
 		}