Sanity checks before writing

SabreTools.IO/Extensions/BinaryWriterExtensions.cs

@@ -410,6 +410,10 @@ namespace SabreTools.IO.Extensions
         /// </summary>
         private static bool WriteFromBuffer(BinaryWriter writer, byte[] value)
         {
+            // If the stream is not writable
+            if (!writer.BaseStream.CanWrite)
+                return false;
+
             // Handle the 0-byte case
             if (value.Length == 0)
                 return true;

SabreTools.IO/Extensions/StreamWriterExtensions.cs

@@ -408,6 +408,10 @@ namespace SabreTools.IO.Extensions
         /// </summary>
         private static bool WriteFromBuffer(Stream stream, byte[] value)
         {
+            // If the stream is not writable
+            if (!stream.CanWrite)
+                return false;
+
             // Handle the 0-byte case
             if (value.Length == 0)
                 return true;