oox: these getShape() functions can be const

Change-Id: Ib0ecffa05b417072c463081691b553d04cf39c9e
Reviewed-on: https://gerrit.libreoffice.org/37914Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

oox/source/shape/LockedCanvasContext.hxx

@@ -27,7 +27,7 @@ public:
 
     oox::core::ContextHandlerRef onCreateContext(sal_Int32 Element, const ::oox::AttributeList& rAttribs) override;
 
-    const oox::drawingml::ShapePtr& getShape()
+    const oox::drawingml::ShapePtr& getShape() const
     {
         return mpShape;
     }

oox/source/shape/WpgContext.hxx

@@ -27,7 +27,7 @@ public:
 
     oox::core::ContextHandlerRef onCreateContext(sal_Int32 nElementToken, const oox::AttributeList& rAttribs) override;
 
-    const oox::drawingml::ShapePtr& getShape()
+    const oox::drawingml::ShapePtr& getShape() const
     {
         return mpShape;
     }

oox/source/shape/WpsContext.hxx

@@ -27,7 +27,7 @@ public:
 
     oox::core::ContextHandlerRef onCreateContext(sal_Int32 nElementToken, const oox::AttributeList& rAttribs) override;
 
-    const oox::drawingml::ShapePtr& getShape()
+    const oox::drawingml::ShapePtr& getShape() const
     {
         return mpShape;
     }