Revert "Allow undo after file reload and don't purge undo buffer"

This commit makes a performance issue: Re-loading the same text file over and over results in huge memory taken up
This reverts commit 198cf90c16.
Fix #5595

PowerEditor/src/ScitillaComponent/Buffer.cpp

@@ -674,7 +674,7 @@ bool FileManager::reloadBuffer(BufferID id)
 	buf->setLoadedDirty(false);	// Since the buffer will be reloaded from the disk, and it will be clean (not dirty), we can set _isLoadedDirty false safetly.
 								// Set _isLoadedDirty false before calling "_pscratchTilla->execute(SCI_CLEARALL);" in loadFileData() to avoid setDirty in SCN_SAVEPOINTREACHED / SCN_SAVEPOINTLEFT
 
-	bool res = loadFileData(doc, buf->getFullPathName(), data, &UnicodeConvertor, loadedFileFormat, false);
+	bool res = loadFileData(doc, buf->getFullPathName(), data, &UnicodeConvertor, loadedFileFormat);
 	buf->_canNotify = true;
 
 	if (res)
@@ -1261,7 +1261,7 @@ LangType FileManager::detectLanguageFromTextBegining(const unsigned char *data,
 	return L_TEXT;
 }
 
-bool FileManager::loadFileData(Document doc, const TCHAR * filename, char* data, Utf8_16_Read * unicodeConvertor, LoadedFileFormat& fileFormat, bool purgeUndoBuffer)
+bool FileManager::loadFileData(Document doc, const TCHAR * filename, char* data, Utf8_16_Read * unicodeConvertor, LoadedFileFormat& fileFormat)
 {
 	FILE *fp = generic_fopen(filename, TEXT("rb"));
 	if (not fp)
@@ -1295,12 +1295,6 @@ bool FileManager::loadFileData(Document doc, const TCHAR * filename, char* data,
 	{
 		_pscratchTilla->execute(SCI_SETREADONLY, false);
 	}
-
-	if (!purgeUndoBuffer)
-	{
-		_pscratchTilla->execute(SCI_BEGINUNDOACTION);
-	}
-
 	_pscratchTilla->execute(SCI_CLEARALL);
 
 
@@ -1433,7 +1427,7 @@ bool FileManager::loadFileData(Document doc, const TCHAR * filename, char* data,
 		fileFormat._eolFormat = format;
 	}
 
-	_pscratchTilla->execute(purgeUndoBuffer ? SCI_EMPTYUNDOBUFFER : SCI_ENDUNDOACTION);
+	_pscratchTilla->execute(SCI_EMPTYUNDOBUFFER);
 	_pscratchTilla->execute(SCI_SETSAVEPOINT);
 
 	if (ro)

PowerEditor/src/ScitillaComponent/Buffer.h

@@ -122,7 +122,7 @@ private:
 	};
 	~FileManager();
 	int detectCodepage(char* buf, size_t len);
-	bool loadFileData(Document doc, const TCHAR* filename, char* buffer, Utf8_16_Read* UnicodeConvertor, LoadedFileFormat& fileFormat, bool purgeUndoBuffer = true);
+	bool loadFileData(Document doc, const TCHAR* filename, char* buffer, Utf8_16_Read* UnicodeConvertor, LoadedFileFormat& fileFormat);
 	LangType detectLanguageFromTextBegining(const unsigned char *data, size_t dataLen);