clear info on new package

This avoids seeing the old info for a short time when browsing another
package. This also avoids seeing the old info when a package is not found
(for example 0.18 packages released after 0.19).

manifest.json

@@ -1,7 +1,7 @@
 {
     "manifest_version": 2,
     "name": "Elm Package Info",
-    "version": "1.7",
+    "version": "1.8",
     "description": "Display additional information for a package on package.elm-lang.org (install command, elm version, license, …)",
     "icons": {
         "16": "icons/elm-16.png",

package.js

@@ -133,12 +133,18 @@ function updatePackageInfo(pkg, elmJson) {
     }
     content.appendChild(dependencies);
 
-    while (info.firstChild) {
-        info.removeChild(info.firstChild);
-    }
+    removeChildren(info);
     info.appendChild(content);
 }
 
+function removeChildren(element) {
+    if (element) {
+        while (element.firstChild) {
+            element.removeChild(element.firstChild);
+        }
+    }
+}
+
 function createCopyToClipboardIcon() {
     const svgNS = "http://www.w3.org/2000/svg";
     const svg = document.createElementNS(svgNS, "svg");
@@ -306,6 +312,7 @@ chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
             }
         } else if (packageChanged(pkg, newPkg)) {
             resetFooterTranslation();
+            removeChildren(info);
             update(newPkg);
             pkg = newPkg;
         }