oox: fix invalid mime type "image/tif"

(regression from ccfc02f7)

Change-Id: I29a366228bf08f29edfa4a8e963889e34aa3d2ea
(cherry picked from commit f18ca153)
Reviewed-on: https://gerrit.libreoffice.org/17144Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>
Tested-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>

oox/source/export/drawingml.cxx

@@ -849,7 +849,7 @@ OUString DrawingML::WriteImage( const Graphic& rGraphic , bool bRelPathToMedia )
             pExtension = ".png";
             break;
         case GFX_LINK_TYPE_NATIVE_TIF:
-            sMediaType = "image/tif";
+            sMediaType = "image/tiff";
             pExtension = ".tif";
             break;
         case GFX_LINK_TYPE_NATIVE_WMF:

sw/qa/extras/ooxmlexport/ooxmlexport5.cxx

@@ -209,7 +209,7 @@ DECLARE_OOXMLEXPORT_TEST(testContentTypeTIF, "fdo77476.docx")
     if (!pXmlDoc)
        return;
 
-    assertXPath(pXmlDoc, "/ContentType:Types/ContentType:Override[@ContentType='image/tif']", "PartName", "/word/media/image1.tif");
+    assertXPath(pXmlDoc, "/ContentType:Types/ContentType:Override[@ContentType='image/tiff']", "PartName", "/word/media/image1.tif");
 }
 
 DECLARE_OOXMLEXPORT_TEST(testFDO77117, "fdo77117.docx")