Try to fix Color picker of lists is empty. Part 2.

Thanks to bronger and xet7 !

Related #3418

packages/wekan-oidc/oidc_server.js

@@ -1,10 +1,12 @@
 Oidc = {};
 httpCa = false;
 
-if (process.env.OAUTH2_CA_CERT.length > 0) {
+if (process.env.OAUTH2_CA_CERT !== undefined) {
     try {
         const fs = Npm.require('fs');
-	httpCa = fs.readFileSync(process.env.OAUTH2_CA_CERT);
+        if (fs.existsSync(process.env.OAUTH2_CA_CERT) {
+          httpCa = fs.readFileSync(process.env.OAUTH2_CA_CERT);
+        }
     } catch(e) {
 	console.log('WARNING: failed loading: ' + process.env.OAUTH2_CA_CERT);
 	console.log(e);