Added some protections to TImageManager.ProcessImagesInRTF in case it…

… is called incorrectly

Although the bug describe in issue #644 (Export Notes Crash - Error Message and Application Freeze During Text Notes Export )
was fixed in the commit fddc38b (Fixed some bugs related to Export and UNICODE (see details)), this new changes
introduce some controls to avoid the consequences of that bug (a runaway pointer)

editor/kn_ImagesMng.pas

@@ -2762,8 +2762,14 @@ function TImageManager.ProcessImagesInRTF(const Buffer: Pointer; BufSize: intege
    In_shppict:= false;
 
 
+   Result:= '';
    RTFText:= PAnsiChar(Buffer);
 
+   if (assigned(Note) and Note.PlainText) or (Length(RTFText) > BufSize) then begin
+      assert(Length(RTFText) <= BufSize );
+      exit;
+   end;
+
    assert(Length(RTFText) <= BufSize );
 
    // fExtenalImagesManager <> nil : We are processing note images from a file we are merging (see MergeFromKNTFile)
@@ -3033,6 +3039,11 @@ function TImageManager.ProcessImagesInRTF(const Buffer: Pointer; BufSize: intege
 
             if (fStorageMode <> smEmbRTF) then begin
                if (ImgID = 0) and ((ImageMode = imImage) or UseExtenalImagesManager) and (Stream <> nil) and (Stream.Size > 0) then begin
+                  if Note = nil then begin
+                     assert(Note <> nil);
+                     Exit('');       // It shouldn't happen, but if it does, we are exporting notes. We leave without processing anything
+                  end;
+
                   if Img <> nil then begin            // Processing images from MergeFromKNTFile
                     ImgCaption:= Img.Caption;
                     if CheckRegisterImage (Stream, Img.ImageFormat,  Width, Height, Note, Img.OriginalPath, Img.IsOwned, 'MergeKNT', Img) then begin