Add nullchecks for typeRoots, remove getCurrentDirectory from ServerHost as it is always the installation location

Author: zhengbli

src/compiler/program.ts

@@ -242,7 +242,7 @@ namespace ts {
         const failedLookupLocations: string[] = [];
 
         // Check primary library paths
-        if (typeRoots.length) {
+        if (typeRoots && typeRoots.length) {
             if (traceEnabled) {
                 trace(host, Diagnostics.Resolving_with_primary_search_path_0, typeRoots.join(", "));
             }
@@ -1060,9 +1060,11 @@ namespace ts {
         let result: string[] = [];
         if (host.directoryExists && host.getDirectories) {
             const typeRoots = getEffectiveTypeRoots(options, host);
-            for (const root of typeRoots) {
-                if (host.directoryExists(root)) {
-                    result = result.concat(host.getDirectories(root));
+            if (typeRoots) {
+                for (const root of typeRoots) {
+                    if (host.directoryExists(root)) {
+                        result = result.concat(host.getDirectories(root));
+                    }
                 }
             }
         }

src/server/editorServices.ts

@@ -113,7 +113,6 @@ namespace ts.server {
             this.moduleResolutionHost = {
                 fileExists: fileName => this.fileExists(fileName),
                 readFile: fileName => this.host.readFile(fileName),
-                getCurrentDirectory: () => this.host.getCurrentDirectory(),
                 directoryExists: directoryName => this.host.directoryExists(directoryName)
             };
         }