sd: fix crash in character format dialog:

When text with different fonts is selected in Draw or Impress, the
character format dialog crashes, because (among other things) the
selected text is not returned by SfxViewShell::GetSelectionText().
Crash was observed both with GraphicViewShellBase and
ImpressViewShellBase as current shell.
Override that method in sd::ViewShellBase to forward to a main shell
that happens to be a DrawViewShell which is not actually a SfxViewShell
but happens to implement GetSelectionText() for mysterious reasons.

sd/source/ui/inc/ViewShellBase.hxx

@@ -123,6 +123,10 @@ public:
     */
     virtual void GetState (SfxItemSet& rSet);
 
+    /* override these from SfxViewShell */
+    virtual String GetSelectionText(sal_Bool);
+    virtual sal_Bool HasSelection(sal_Bool) const;
+
     SvBorder GetBorder (bool bOuterResize);
     virtual void InnerResizePixel (const Point& rOrigin, const Size& rSize);
     virtual void OuterResizePixel (const Point& rOrigin, const Size& rSize);

sd/source/ui/view/ViewShellBase.cxx

@@ -489,7 +489,25 @@ void ViewShellBase::InitializeFramework (void)
 }
 
 
+String ViewShellBase::GetSelectionText(sal_Bool bCompleteWords)
+{
+    ::boost::shared_ptr<ViewShell> const pMainShell(GetMainViewShell());
+    DrawViewShell *const pDrawViewShell(
+            dynamic_cast<DrawViewShell*>(pMainShell.get()));
+    return (pDrawViewShell)
+        ?   pDrawViewShell->GetSelectionText(bCompleteWords)
+        :   SfxViewShell::GetSelectionText(bCompleteWords);
+}
 
+sal_Bool ViewShellBase::HasSelection(sal_Bool bText) const
+{
+    ::boost::shared_ptr<ViewShell> const pMainShell(GetMainViewShell());
+    DrawViewShell *const pDrawViewShell(
+            dynamic_cast<DrawViewShell*>(pMainShell.get()));
+    return (pDrawViewShell)
+        ?   pDrawViewShell->HasSelection(bText)
+        :   SfxViewShell::HasSelection(bText);
+}
 
 void ViewShellBase::InnerResizePixel (const Point& rOrigin, const Size &rSize)
 {