improve const-correctness in ScCaptionPtr

mostly to make my passstuffbyref loplugin happier

Change-Id: I148b6b418100de860dfc49aaec6c544d0fe14c72
Reviewed-on: https://gerrit.libreoffice.org/47225Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

sc/inc/postit.hxx

@@ -52,9 +52,12 @@ public:
     ScCaptionPtr& operator=( const ScCaptionPtr& r );
     ScCaptionPtr& operator=( ScCaptionPtr&& r );
     explicit operator bool() const    { return mpCaption != nullptr; }
-    SdrCaptionObj* get() const        { return mpCaption; }
-    SdrCaptionObj* operator->() const { return mpCaption; }
-    SdrCaptionObj& operator*() const  { return *mpCaption; }
+    const SdrCaptionObj* get() const        { return mpCaption; }
+    SdrCaptionObj* get()        { return mpCaption; }
+    const SdrCaptionObj* operator->() const { return mpCaption; }
+    SdrCaptionObj* operator->() { return mpCaption; }
+    const SdrCaptionObj& operator*() const  { return *mpCaption; }
+    SdrCaptionObj& operator*()  { return *mpCaption; }
 
     // Does not default to nullptr to make it visually obvious where such is used.
     void reset( SdrCaptionObj* p );

sc/source/core/data/postit.cxx

@@ -401,7 +401,7 @@ public:
     /** Create a new caption object and inserts it into the document. */
     explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScNoteData& rNoteData );
     /** Manipulate an existing caption. */
-    explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, const ScCaptionPtr& xCaption, bool bShown );
+    explicit            ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption, bool bShown );
 };
 
 ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScNoteData& rNoteData ) :
@@ -425,7 +425,7 @@ ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& r
     }
 }
 
-ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, const ScCaptionPtr& xCaption, bool bShown ) :
+ScNoteCaptionCreator::ScNoteCaptionCreator( ScDocument& rDoc, const ScAddress& rPos, ScCaptionPtr& xCaption, bool bShown ) :
     ScCaptionCreator( rDoc, rPos, xCaption )
 {
     SdrPage* pDrawPage = GetDrawPage();