tdf#119756 assume the HFONT is always valid

This is a regression from the commit 7cb3e475 ("WIN add
SalGraphics* to WinFontInstance"). We need a sensible way to
compare the SalGraphics / HFONT. I'm not sure how to implement
this yet, so just assume unchanged, as the old code did.

Change-Id: I828a41e529976c500eedaef3afd40cf20287f746
Reviewed-on: https://gerrit.libreoffice.org/60256
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

vcl/win/gdi/winlayout.cxx

@@ -395,10 +395,9 @@ hb_font_t* WinFontInstance::ImplInitHbFont()
 
 void WinFontInstance::SetGraphics(WinSalGraphics *pGraphics)
 {
-    ReleaseHbFont();
-    if (m_hFont)
-        ::DeleteFont(m_hFont);
     m_pGraphics = pGraphics;
+    if (m_hFont)
+        return;
     HFONT hOrigFont;
     m_hFont = m_pGraphics->ImplDoSetFont(GetFontSelectPattern(), GetFontFace(), m_fScale, hOrigFont);
     SelectObject(m_pGraphics->getHDC(), hOrigFont);