Fix undefined behavior in sign conversion. 
https://github.com/mpruett/audiofile/commit/b62c902dd258125cac86cd2df21fc898035a43d3

Index: libaudiofile/modules/SimpleModule.h
--- libaudiofile/modules/SimpleModule.h.orig
+++ libaudiofile/modules/SimpleModule.h
@@ -123,7 +123,8 @@ struct signConverter
 	typedef typename IntTypes<Format>::UnsignedType UnsignedType;
 
 	static const int kScaleBits = (Format + 1) * CHAR_BIT - 1;
-	static const int kMinSignedValue = -1 << kScaleBits;
+	static const int kMaxSignedValue = (((1 << (kScaleBits - 1)) - 1) << 1) + 1;
+	static const int kMinSignedValue = -kMaxSignedValue - 1;
 
 	struct signedToUnsigned : public std::unary_function<SignedType, UnsignedType>
 	{
