Add undefined check throughout app

Removes both "no execute _computeDiffURL before patchNum is knwon"
and "gr-linked-text with null config" tests.

This is due to behaviour changes in Polymer2 which means functions are
always called regardless if one of the params is undefined.

Change-Id: I4bdbe03f9dc46d03a8d0997055271327f0c2a2ea

polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.js

@@ -891,6 +891,7 @@
      * than SYNTAX_MAX_LINE_LENGTH.
      */
     _anyLineTooLong(diff) {
+      if (!diff) return false;
       return diff.content.some(section => {
         const lines = section.ab ?
               section.ab :

polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js

@@ -265,7 +265,8 @@
 
     _getFiles(changeNum, patchRangeRecord) {
       // Polymer 2: check for undefined
-      if ([changeNum, patchRangeRecord].some(arg => arg === undefined)) {
+      if ([changeNum, patchRangeRecord, patchRangeRecord.base]
+          .some(arg => arg === undefined)) {
         return;
       }
 
@@ -745,6 +746,9 @@
     },
 
     _getDiffUrl(change, patchRange, path) {
+      if ([change, patchRange, path].some(arg => arg === undefined)) {
+        return '';
+      }
       return Gerrit.Nav.getUrlForDiff(change, path, patchRange.patchNum,
           patchRange.basePatchNum);
     },
@@ -783,6 +787,9 @@
     },
 
     _getChangePath(change, patchRange, revisions) {
+      if ([change, patchRange].some(arg => arg === undefined)) {
+        return '';
+      }
       const range = this._getChangeUrlRange(patchRange, revisions);
       return Gerrit.Nav.getUrlForChange(change, range.patchNum,
           range.basePatchNum);

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.js

@@ -967,6 +967,7 @@
      * @return {number}
      */
     getDiffLength(diff) {
+      if (!diff) return 0;
       return diff.content.reduce((sum, sec) => {
         if (sec.hasOwnProperty('ab')) {
           return sum + sec.ab.length;