various Readers: Fix GetCache return type

Tests: fix ImageWriter cache type

src/ImageReader.h

@@ -48,6 +48,8 @@
 
 namespace openshot
 {
+	// Forward decls
+	class CacheBase;
 
 	/**
 	 * @brief This class uses the ImageMagick++ libraries, to open image files, and return
@@ -90,7 +92,7 @@ namespace openshot
 		void Close() override;
 
 		/// Get the cache object used by this reader (always returns NULL for this object)
-		CacheMemory* GetCache() override { return NULL; };
+		CacheBase* GetCache() override { return NULL; };
 
 		/// Get an openshot::Frame object for a specific frame number of this reader.  All numbers
 		/// return the same Frame, since they all share the same image data.

src/QtHtmlReader.h

@@ -49,6 +49,8 @@ class QImage;
 
 namespace openshot
 {
+	// Forward decls
+	class CacheBase;
 
 	/**
 	 * @brief This class uses Qt libraries, to create frames with rendered HTML, and return
@@ -115,7 +117,7 @@ namespace openshot
 		void Close() override;
 
 		/// Get the cache object used by this reader (always returns NULL for this object)
-		openshot::CacheMemory* GetCache() override { return NULL; };
+		CacheBase* GetCache() override { return NULL; };
 
 		/// Get an openshot::Frame object for a specific frame number of this reader.  All numbers
 		/// return the same Frame, since they all share the same image data.

src/QtImageReader.h

@@ -42,6 +42,8 @@
 
 namespace openshot
 {
+	// Forward decl
+	class CacheBase;
 
 	/**
 	 * @brief This class uses the Qt library, to open image files, and return
@@ -88,7 +90,7 @@ namespace openshot
 		void Close() override;
 
 		/// Get the cache object used by this reader (always returns NULL for this object)
-		CacheMemory* GetCache() override { return NULL; };
+		CacheBase* GetCache() override { return NULL; };
 
 		/// Get an openshot::Frame object for a specific frame number of this reader.  All numbers
 		/// return the same Frame, since they all share the same image data.

src/QtTextReader.h

@@ -49,6 +49,8 @@ class QImage;
 
 namespace openshot
 {
+	// Forward decls
+	class CacheBase;
 
 	/**
 	 * @brief This class uses Qt libraries, to create frames with "Text", and return
@@ -126,7 +128,7 @@ namespace openshot
 		void Close() override;
 
 		/// Get the cache object used by this reader (always returns NULL for this object)
-		openshot::CacheMemory* GetCache() override { return NULL; };
+		CacheBase* GetCache() override { return NULL; };
 
 		/// Get an openshot::Frame object for a specific frame number of this reader.  All numbers
 		/// return the same Frame, since they all share the same image data.

tests/ImageWriter_Tests.cpp

@@ -85,7 +85,7 @@ TEST(Gif)
 	// Basic Reader state queries
 	CHECK_EQUAL("ImageReader", r1.Name());
 
-	CacheMemory* c = r1.GetCache();
+	CacheBase* c = r1.GetCache();
 	CHECK_EQUAL(true, c == nullptr);
 
 	CHECK_EQUAL(false, r1.IsOpen());