luci-base: fix tab handling in modal dialogues

When adding tabs in modal dialogues, the old code of simply assigning
s.tabs = this.tabs was problematic because it was an array of objects
whose behaviour would cause a traceback when s.tab is called in e.g.
a protocol handler Modal when it was reopened.

Now verify the properties do not already exist before assigning them.

This means one can define s.tab(...) in a Modal UI without a try
block (which would even then sometimes fail).

Signed-off-by: Paul Donald <newtwen+github@gmail.com>

Author: systemcrash

modules/luci-base/htdocs/luci-static/resources/form.js

@@ -3339,8 +3339,26 @@ const CBITableSection = CBITypedSection.extend(/** @lends LuCI.form.TableSection
 			m.section = section_id;
 			m.readonly = parent.readonly;
 
-			s.tabs = this.tabs;
-			s.tab_names = this.tab_names;
+			/* Clone tabs as both array and object. Otherwise calling renderMoreOptionsModal (reopening
+			the same Modal multiple times) results in errors when s.tab is called in the modal. This
+			allows Modal dialogues that declare new tabs to be opened multiple times without re-creating
+			tabs that 'already exist'. */
+			if (this.tabs) {
+				s.tabs = Array.from(this.tabs);
+				for (const key in this.tabs) {
+					if (Object.prototype.hasOwnProperty.call(this.tabs, key) && isNaN(Number(key))) {
+						s.tabs[key] = this.tabs[key];
+					}
+				}
+			} else {
+				s.tabs = undefined;
+			}
+
+			if (this.tab_names) {
+				s.tab_names = Array.isArray(this.tab_names) ? this.tab_names.slice() : Object.assign({}, this.tab_names);
+			} else {
+				s.tab_names = undefined;
+			}
 
 			this.cloneOptions(this, s);