Fix lexer crash when given undefined

src/LanguageServer.ts

@@ -526,7 +526,7 @@ export class LanguageServer {
             timestamp: Date.now(),
             index: this.busyStatusIndex,
             activeRuns: [...this.projectManager.busyStatusTracker.activeRuns]
-        }).catch(logAndIgnoreError);
+        })?.catch(logAndIgnoreError);
     }
     private busyStatusIndex = -1;
 

src/files/BrsFile.spec.ts

@@ -47,6 +47,15 @@ describe('BrsFile', () => {
         program.dispose();
     });
 
+    describe('dispose', () => {
+        it('does not crash the program after it has been disposed', () => {
+            const file = program.setFile('source/main.bs', `sub main(): end sub`);
+            file.dispose();
+            program.validate();
+            expectZeroDiagnostics(program);
+        });
+    });
+
     describe('allowBrighterScriptInBrightScript', () => {
         it('is false by default', () => {
             program.setFile('source/main.brs', `

src/lexer/Lexer.ts

@@ -126,7 +126,7 @@ export class Lexer {
      * @returns `true` if the lexer has read to (or past) the end of its input, otherwise `false`.
      */
     private isAtEnd() {
-        return this.current >= this.source.length;
+        return !this.source || this.current >= this.source.length;
     }
 
     /**