guess at possible bug in #192

it may be that we try reading a corrupted os/2 table, hard to tell without test document.

src/UglyToad.PdfPig.Fonts/TrueType/Parser/Os2TableParser.cs

@@ -67,11 +67,42 @@
                     lastCharacterIndex);
             }
 
-            var sTypoAscender = data.ReadSignedShort();
+            short sTypoAscender;
-            var sTypoDescender = data.ReadSignedShort();
+            short sTypoDescender;
-            var sTypoLineGap = data.ReadSignedShort();
+            short sTypoLineGap;
-            var usWinAscent = data.ReadUnsignedShort();
+            ushort usWinAscent;
-            var usWinDescent = data.ReadUnsignedShort();
+            ushort usWinDescent;
+
+            try
+            {
+                sTypoAscender = data.ReadSignedShort();
+                sTypoDescender = data.ReadSignedShort();
+                sTypoLineGap = data.ReadSignedShort();
+                usWinAscent = data.ReadUnsignedShort();
+                usWinDescent = data.ReadUnsignedShort();
+            }
+            catch
+            {
+                // Font may be invalid. Try falling back to shorter version...
+                return new Os2Table(header, version, xAvgCharWidth,
+                    weightClass, widthClass, typeFlags, ySubscriptXSize,
+                    ySubscriptYSize,
+                    ySubscriptXOffset,
+                    ySubscriptYOffset,
+                    ySuperscriptXSize,
+                    ySuperscriptYSize,
+                    ySuperscriptXOffset,
+                    ySuperscriptYOffset,
+                    yStrikeoutSize,
+                    yStrikeoutPosition,
+                    familyClass,
+                    panose,
+                    unicodeCharRange,
+                    vendorId,
+                    selectionFlags,
+                    firstCharacterIndex,
+                    lastCharacterIndex);
+            }
 
             if (version == 0)
             {