only allow IMG tag when selecting single tag (fix #1800)

src/ui/content/content-ui.js

@@ -227,8 +227,10 @@ function markSelectedContent() {
 						markSelectedNode(treeWalker.currentNode);
 					}
 					if (range.startContainer === range.endContainer && selection.rangeCount == 1 && range.startOffset == 0 && range.endOffset == 0) {
-						selectionFound = true;
-						markSelectedNode(treeWalker.currentNode);
+						if (range.startContainer.tagName === "IMG" || range.startContainer.tagName === "VIDEO") {
+							selectionFound = true;
+							markSelectedNode(treeWalker.currentNode);
+						}
 					}
 				}
 				if (selectionFound && treeWalker.currentNode == range.startContainer) {