tdf#165606 fix: master slide panel doesn't resized correctly in gtk

- follow up to 98b86bff2c73
- the problem was get_rect give 0 height when preview are loading.
- this patch fixes the problem by taking image size from
MasterPageContainer

Change-Id: Ie4a3e25826e871ae5cbda58edba092e9a3eae193
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/182806
Reviewed-by: Tomaž Vajngerl <[email protected]>
Tested-by: Jenkins
(cherry picked from commit 60cfd11276d6cef6f796f7b45ae1da8a29bbe430)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/183162
Tested-by: Jenkins CollaboraOffice <[email protected]>
(cherry picked from commit fef5fa64b947f39260389a74ee4ac9f267300d08)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/183161

Author: Rash419

sd/source/ui/sidebar/MasterPageContainer.hxx

@@ -76,7 +76,7 @@ public:
 
     /** Return the preview size in pixels.
     */
-    Size const& GetPreviewSizePixel() const;
+    const Size& GetPreviewSizePixel() const;
 
     enum PreviewState
     {

sd/source/ui/sidebar/MasterPagesSelector.cxx

@@ -586,7 +586,8 @@ css::ui::LayoutSize MasterPagesSelector::GetHeightForWidth(const sal_Int32 nWidt
 {
     // there is no way to get margin of item programatically, we use value provided in ui file.
     const int nMargin = 6;
-    sal_Int32 nColumnCount = nWidth / (mxPreviewIconView->get_item_width() + (5 * nMargin));
+    const Size& previewSize = mpContainer->GetPreviewSizePixel();
+    sal_Int32 nColumnCount = nWidth / (previewSize.Width() + (2 * nMargin));
     if (nColumnCount < 1)
         nColumnCount = 1;
 
@@ -595,8 +596,7 @@ css::ui::LayoutSize MasterPagesSelector::GetHeightForWidth(const sal_Int32 nWidt
     if (nRowCount < 1)
         nRowCount = 1;
 
-    sal_Int32 nPreferedHeight
-        = nRowCount * (mxPreviewIconView->get_rect(nTotalItems - 1).GetHeight() + (2 * nMargin));
+    sal_Int32 nPreferedHeight = nRowCount * (previewSize.getHeight() + (4 * nMargin));
     return css::ui::LayoutSize(nPreferedHeight, nPreferedHeight, nPreferedHeight);
 }