fixed importFilter::readByte() to return proper integer instead of signed char - makes import-filters finally work

git-svn-id: https://lmms.svn.sf.net/svnroot/lmms/trunk/lmms@742 0778d3d1-df1d-0410-868b-ea421aaaa00d

include/import_filter.h

@@ -67,8 +67,8 @@ protected:
 
 	inline int readByte( void )
 	{
-		char c;
-		if( m_file.getChar( &c ) )
+		unsigned char c;
+		if( m_file.getChar( (char*) &c ) )
 		{
 			return( static_cast<int>( c ) );
 		}