sw XHTML export: fix missing type attribute for fallback image

This was working in OutHTML_FrameFormatGrfNode(), but not in
OutHTML_FrameFormatOLENodeGrf().

Change-Id: I4f8e280713cad2a00cad5da65a09afc5a36d40d0
Reviewed-on: https://gerrit.libreoffice.org/51571Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

sw/qa/extras/htmlexport/htmlexport.cxx

@@ -406,6 +406,18 @@ DECLARE_HTMLEXPORT_ROUNDTRIP_TEST(testReqIfOleImg, "reqif-ole-img.xhtml")
 
     // Check alternate text (it was empty, for export the 'alt' attribute was used).
     CPPUNIT_ASSERT_EQUAL(OUString("OLE Object"), getProperty<OUString>(xObject, "Title").trim());
+
+    if (!mbExported)
+        return;
+
+    // "type" attribute was missing for the inner <object> element.
+    SvStream* pStream = maTempFile.GetStream(StreamMode::READ);
+    CPPUNIT_ASSERT(pStream);
+    pStream->Seek(STREAM_SEEK_TO_END);
+    sal_uInt64 nLength = pStream->Tell();
+    pStream->Seek(0);
+    OString aStream(read_uInt8s_ToOString(*pStream, nLength));
+    CPPUNIT_ASSERT(aStream.indexOf("type=\"image/png\"") != -1);
 }
 
 DECLARE_HTMLEXPORT_ROUNDTRIP_TEST(testReqIfPngImg, "reqif-png-img.xhtml")

sw/source/filter/html/htmlplug.cxx

@@ -1448,16 +1448,26 @@ Writer& OutHTML_FrameFormatOLENodeGrf( Writer& rWrt, const SwFrameFormat& rFrame
     }
 
     OUString aGraphicURL;
+    OUString aMimeType;
     if(!rHTMLWrt.mbEmbedImages)
     {
         const OUString* pTempFileName = rHTMLWrt.GetOrigFileName();
         if(pTempFileName)
             aGraphicURL = *pTempFileName;
 
+        OUString aFilterName("JPG");
+        XOutFlags nFlags = XOutFlags::UseGifIfPossible | XOutFlags::UseNativeIfPossible;
+
+        if (bObjectOpened)
+        {
+            aFilterName = "PNG";
+            nFlags = XOutFlags::NONE;
+            aMimeType = "image/png";
+        }
+
         ErrCode nErr = XOutBitmap::WriteGraphic( aGraphic, aGraphicURL,
-                                    "JPG",
-                                    (XOutFlags::UseGifIfPossible |
-                                     XOutFlags::UseNativeIfPossible) );
+                                    aFilterName,
+                                    nFlags );
         if( nErr )              // error, don't write anything
         {
             rHTMLWrt.m_nWarn = WARN_SWG_POOR_LOAD;
@@ -1474,7 +1484,7 @@ Writer& OutHTML_FrameFormatOLENodeGrf( Writer& rWrt, const SwFrameFormat& rFrame
         nFlags |= HtmlFrmOpts::Replacement;
     OutHTML_Image( rWrt, rFrameFormat, aGraphicURL, aGraphic,
             pOLENd->GetTitle(), pOLENd->GetTwipSize(),
-            nFlags, "ole" );
+            nFlags, "ole", nullptr, aMimeType );
 
     if (bObjectOpened)
         // Close native data.