Fix a potential undefined behaviour & improve some codes

- init grabSize
- optimize WcharMbcsConvertor instance set
- remove unused var in TreeView::searchLeafRecusivelyAndBuildTree()
- missing nullpointer check in ScintillaEditView::init()

Close #14844

PowerEditor/src/ScintillaComponent/Buffer.cpp

@@ -1054,7 +1054,7 @@ bool FileManager::backupCurrentBuffer()
 				else
 				{
 					WcharMbcsConvertor& wmc = WcharMbcsConvertor::getInstance();
-					size_t grabSize;
+					size_t grabSize = 0;
 					for (size_t i = 0; i < lengthDoc; i += grabSize)
 					{
 						grabSize = lengthDoc - i;
@@ -1209,14 +1209,14 @@ SavingStatus FileManager::saveBuffer(BufferID id, const TCHAR* filename, bool is
 		}
 		else
 		{
-			WcharMbcsConvertor& wmc = WcharMbcsConvertor::getInstance();
 			if (lengthDoc == 0)
 			{
 				isWrittenSuccessful = UnicodeConvertor.writeFile(buf, 0);
 			}
 			else
 			{
-				size_t grabSize;
+				WcharMbcsConvertor& wmc = WcharMbcsConvertor::getInstance();
+				size_t grabSize = 0;
 				for (size_t i = 0; i < lengthDoc; i += grabSize)
 				{
 					grabSize = lengthDoc - i;

PowerEditor/src/ScintillaComponent/ScintillaEditView.cpp

@@ -340,10 +340,13 @@ void ScintillaEditView::init(HINSTANCE hInst, HWND hPere)
 	{
 		auto defaultCharListLen = execute(SCI_GETWORDCHARS);
 		char *defaultCharList = new char[defaultCharListLen + 1];
-		execute(SCI_GETWORDCHARS, 0, reinterpret_cast<LPARAM>(defaultCharList));
-		defaultCharList[defaultCharListLen] = '\0';
-		_defaultCharList = defaultCharList;
-		delete[] defaultCharList;
+		if(defaultCharList)
+		{
+			execute(SCI_GETWORDCHARS, 0, reinterpret_cast<LPARAM>(defaultCharList));
+			defaultCharList[defaultCharListLen] = '\0';
+			_defaultCharList = defaultCharList;
+			delete[] defaultCharList;
+		}
 	}
 	//Get the startup document and make a buffer for it so it can be accessed like a file
 	attachDefaultDoc();

PowerEditor/src/WinControls/TreeView/TreeView.cpp

@@ -660,14 +660,12 @@ bool TreeView::searchLeafRecusivelyAndBuildTree(HTREEITEM tree2Build, const gene
 		}
 	}
 
-	size_t i = 0;
 	bool isOk = true;
 	for (HTREEITEM hItem = getChildFrom(tree2Search); hItem != NULL; hItem = getNextSibling(hItem))
 	{
 		isOk = searchLeafRecusivelyAndBuildTree(tree2Build, text2Search, index2Search, hItem);
 		if (!isOk)
 			break;
-		++i;
 	}
 	return isOk;
 }