Fix bug if previousToken is not an Identifier

Author: Andy Hanson

src/services/completions.ts

@@ -840,7 +840,7 @@ namespace ts.Completions {
             const symbolMeanings = SymbolFlags.Type | SymbolFlags.Value | SymbolFlags.Namespace | SymbolFlags.Alias;
 
             symbols = typeChecker.getSymbolsInScope(scopeNode, symbolMeanings);
-            getSymbolsFromOtherSourceFileExports(symbols, previousToken === undefined ? "" : previousToken.getText());
+            getSymbolsFromOtherSourceFileExports(symbols, previousToken && isIdentifier(previousToken) ? previousToken.text : "");
             filterGlobalCompletion(symbols);
 
             return true;

tests/cases/fourslash/completionsImport_previousTokenIsSemicolon.ts

@@ -0,0 +1,11 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: /a.ts
+////export function foo() {}
+
+// @Filename: /b.ts
+////import * as a from 'a';
+/////**/
+
+goTo.marker("");
+verify.completionListContains("foo", "function foo(): void", "", "function", /*spanIndex*/ undefined, /*hasAction*/ true);