Fix the drag marker dimensions in the thumbnails view

STR:
 - open outline view;
 - switch to thumbnails one;
 - start to drag a thumbnail.

test/integration/reorganize_pages_spec.mjs

@@ -486,4 +486,71 @@ describe("Reorganize Pages View", () => {
       );
     });
   });
+
+  describe("Drag marker must have the right non-zero dimensions", () => {
+    let pages;
+
+    beforeEach(async () => {
+      pages = await loadAndWait(
+        "page_with_number_and_link.pdf",
+        "#viewsManagerToggleButton",
+        "1",
+        null,
+        {
+          enableSplitMerge: true,
+          sidebarViewOnLoad: 2 /* = SidebarView.OUTLINES */,
+        }
+      );
+    });
+
+    afterEach(async () => {
+      await closePages(pages);
+    });
+
+    it("should check if the drag marker width is non-zero", async () => {
+      await Promise.all(
+        pages.map(async ([browserName, page]) => {
+          await page.waitForSelector("#outlinesView", { visible: true });
+          await page.waitForSelector("#viewsManagerSelectorButton", {
+            visible: true,
+          });
+          await page.click("#viewsManagerSelectorButton");
+          await page.waitForSelector("#thumbnailsViewMenu", { visible: true });
+          await page.click("#thumbnailsViewMenu");
+
+          const thumbSelector = "#thumbnailsView .thumbnailImage";
+          await page.waitForSelector(thumbSelector, { visible: true });
+          const rect1 = await getRect(page, getThumbnailSelector(1));
+          const rect2 = await getRect(page, getThumbnailSelector(2));
+
+          const handleAddedMarker = await waitForDOMMutation(
+            page,
+            mutationList => {
+              for (const mutation of mutationList) {
+                if (mutation.type !== "childList") {
+                  continue;
+                }
+                for (const node of mutation.addedNodes) {
+                  if (node.classList.contains("dragMarker")) {
+                    const rect = node.getBoundingClientRect();
+                    return rect.width !== 0;
+                  }
+                }
+              }
+              return false;
+            }
+          );
+
+          await dragAndDrop(
+            page,
+            getThumbnailSelector(1),
+            [[0, rect2.y - rect1.y + rect2.height / 2]],
+            10
+          );
+
+          await awaitPromise(handleAddedMarker);
+        })
+      );
+    });
+  });
 });

web/app.js

@@ -388,6 +388,7 @@ const PDFViewerApplication = {
         pageColorsBackground: x => x,
         pageColorsForeground: x => x,
         localeProperties: x => ({ lang: x }),
+        sidebarViewOnLoad: x => parseInt(x),
       });
     }
 

web/pdf_thumbnail_viewer.js

@@ -635,6 +635,10 @@ class PDFThumbnailViewer {
         offsetWidth: w,
         offsetHeight: h,
       } = div;
+      if (w === 0) {
+        // The thumbnail view isn't visible.
+        return;
+      }
       bbox[i * 4] = x;
       bbox[i * 4 + 1] = y;
       bbox[i * 4 + 2] = w;