Bug 1572329 - Fix error that prevented the top history result from being deleted. r=mak

AFAICT this bug isn't reproducible anymore after bug 1623666. i.e., it's no
longer possible to show the history view. You can still see a history-like view
by typing ^ or a space, but in that case the first result is a search result,
not a history result, so it can't be deleted anyway. Nevertheless we should fix
this error.

Differential Revision: https://phabricator.services.mozilla.com/D79576

browser/components/urlbar/UrlbarController.jsm

@@ -593,14 +593,15 @@ class UrlbarController {
     const selectedResult = this.input.view.selectedResult;
     if (
       !selectedResult ||
-      selectedResult.source != UrlbarUtils.RESULT_SOURCE.HISTORY
+      selectedResult.source != UrlbarUtils.RESULT_SOURCE.HISTORY ||
+      selectedResult.heuristic
     ) {
       return false;
     }
 
     let { queryContext } = this._lastQueryContextWrapper;
     let index = queryContext.results.indexOf(selectedResult);
-    if (!index) {
+    if (index < 0) {
       Cu.reportError("Failed to find the selected result in the results");
       return false;
     }