use length from stream dictionary if directly available

when brute forcing we use the length available in the stream's dictionary token if it is a direct number rather than an indirect reference.

src/UglyToad.PdfPig/Tokenization/Scanner/PdfTokenScanner.cs

@@ -233,6 +233,11 @@
             // Get the expected length from the stream dictionary if present.
             long? length = getLength ? GetStreamLength(streamDictionaryToken) : default(long?);
 
+            if (!getLength && streamDictionaryToken.TryGet(NameToken.Length, out NumericToken inlineLengthToken))
+            {
+                length = inlineLengthToken.Long;
+            }
+
             // Verify again that we start with "stream"
             var hasStartStreamToken = ReadStreamTokenStart(inputBytes, startStreamTokenOffset);