Allocation-safe asset reading

Try to not pre-allocate memory during asset reading

AssetStudio/ObjectReader.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 
 namespace AssetStudio
 {
@@ -16,6 +17,8 @@ namespace AssetStudio
 
         public UnityVersion version => assetsFile.version;
 
+        public long Remaining => byteStart + byteSize - Position;
+
         public ObjectReader(EndianBinaryReader reader, SerializedFile assetsFile, ObjectInfo objectInfo) : base(reader.BaseStream, reader.Endian)
         {
             this.assetsFile = assetsFile;
@@ -36,6 +39,12 @@ namespace AssetStudio
             m_Version = assetsFile.header.m_Version;
         }
 
+        public void ThrowIfTooLarge(float val)
+        {
+            if (val < 0 || val > Remaining)
+                throw new EndOfStreamException();
+        }
+
         public void Reset()
         {
             Position = byteStart;