[FIX] web_editor: properly evaluate if a range is an image

The previous implementation apparently came from an old version
of summernote (see odoo@d33086c).

This commits should improve it to handle all known cases.

See odoo#20877

addons/web_editor/static/src/js/summernote.js

@@ -886,34 +886,60 @@ range.WrappedRange.prototype.reRange = function (keep_end, isNotBreakable) {
 
     return new range.WrappedRange(sc, so, ec, eo);
 };
-// isOnImg: judge whether range is an image node or not
+/**
+ * Returns the image the range is in or matches (if any, false otherwise).
+ *
+ * @todo this implementation may not cover all corner cases but should do the
+ * trick for all reproductible ones
+ * @returns {DOMElement|boolean}
+ */
 range.WrappedRange.prototype.isOnImg = function () {
+    // If not a selection but a cursor position, just check if a point's
+    // ancestor is an image or not
+    if (this.sc === this.ec && this.so === this.eo) {
+        return dom.ancestor(this.sc, dom.isImg);
+    }
+
+    var startPoint = {node: this.sc, offset: this.so};
+    var endPoint = {node: this.ec, offset: this.eo};
+
     var nb = 0;
     var image;
-    var startPoint = {node: this.sc.childNodes.length && this.sc.childNodes[this.so] || this.sc};
-    startPoint.offset = startPoint.node === this.sc ? this.so : 0;
-    var endPoint = {node: this.ec.childNodes.length && this.ec.childNodes[this.eo] || this.ec};
-    endPoint.offset = endPoint.node === this.ec ? this.eo : 0;
-
-    if (dom.isImg(startPoint.node)) {
-        nb ++;
-        image = startPoint.node;
-    }
+    var textNode;
     dom.walkPoint(startPoint, endPoint, function (point) {
-        if (!dom.isText(endPoint.node) && point.node === endPoint.node && point.offset === endPoint.offset) {
+        // If the element has children (not a text node and not empty node),
+        // the element cannot be considered as selected (these children will
+        // be processed to determine that)
+        if (dom.hasChildren(point.node)) {
             return;
         }
-        var node = point.node.childNodes.length && point.node.childNodes[point.offset] || point.node;
-        var offset = node === point.node ? point.offset : 0;
-        var isImg = dom.ancestor(node, dom.isImg);
-        if (!isImg && ((!dom.isBR(node) && !dom.isText(node)) || (offset && node.textContent.length !== offset && node.textContent.match(/\S|\u00A0/)))) {
+
+        // Check if an ancestor of the current point is an image
+        var pointImg = dom.ancestor(point.node, dom.isImg);
+        var isText = dom.isText(point.node);
+
+        // Check if a visible element is selected, i.e.
+        // - If an ancestor of the current is an image we did not see yet
+        // - If the point is not in a br or a text (so a node with no children)
+        // - If the point is in a non empty text node we already saw
+        if (pointImg ?
+            (image !== pointImg) :
+            ((!dom.isBR(point.node) && !isText) || (textNode === point.node && point.node.textContent.match(/\S|\u00A0/)))) {
             nb++;
         }
-        if (isImg && image !== isImg) {
-            image = isImg;
-            nb ++;
+
+        // If an ancestor of the current point is an image, then save it as the
+        // image we are looking for
+        if (pointImg) {
+            image = pointImg;
+        }
+        // If the current point is a text node save it as the last text node
+        // seen (if we see it again, this might mean it is selected)
+        if (isText) {
+            textNode = point.node;
         }
     });
+
     return nb === 1 && image;
 };
 range.WrappedRange.prototype.deleteContents = function (towrite) {