[0.4.12][EXPLORER] Properly initialize tbBtn.iBitmap. CORE-14262 PR#1667

In CNotifyToolbar::AddButton tbBtn.iBitmap (imagelist-index)
was initialized with 0. TightVNC adds the icon without NIF_ICON flag.
So the wrong icon index was kept and later replaced.

This fixes an old regression visible since SVN r68893

cherry picked from commit 0.4.13-dev-481-g
8d6c9e8

Author: andy-123

base/shell/explorer/syspager.cpp

@@ -737,6 +737,7 @@ BOOL CNotifyToolbar::AddButton(_In_ CONST NOTIFYICONDATA *iconData)
     tbBtn.dwData = (DWORD_PTR)notifyItem;
     tbBtn.iString = (INT_PTR) text;
     tbBtn.idCommand = GetButtonCount();
+    tbBtn.iBitmap = -1;
 
     if (iconData->uFlags & NIF_STATE)
     {