FrameMapper: Eliminate is_open member variable

It was being used uninitialized because it's never actually set,
therefore it serves no purpose.

include/FrameMapper.h

@@ -138,7 +138,6 @@ namespace openshot
 	 */
 	class FrameMapper : public ReaderBase {
 	private:
-		bool is_open;
 		bool field_toggle;		// Internal odd / even toggle (used when building the mapping)
 		Fraction original;		// The original frame rate
 		Fraction target;		// The target frame rate

src/FrameMapper.cpp

@@ -61,9 +61,9 @@ FrameMapper::FrameMapper(ReaderBase *reader, Fraction target, PulldownType targe
 
 // Destructor
 FrameMapper::~FrameMapper() {
-	if (is_open)
-		// Auto Close if not already
-		Close();
+
+	// Auto Close if not already
+	Close();
 
 	reader = NULL;
 }