Detect compile_commands.json after containing folder deleted and recr…

…eated on Windows (microsoft#13032)

* fix issue microsoft#7030
* check for the undefined case (on first load)

Extension/src/LanguageServer/configurations.ts

@@ -2340,7 +2340,9 @@ export class CppProperties {
                 }
             } else {
                 const compileCommandsLastChanged: Date | undefined = this.compileCommandsFileWatcherFallbackTime.get(compileCommandsFile);
-                if (compileCommandsLastChanged !== undefined && stats.mtime > compileCommandsLastChanged) {
+                if ((this.compileCommandsFile === undefined) ||
+                    (this.compileCommandsFile === null) ||
+                    (compileCommandsLastChanged !== undefined && stats.mtime > compileCommandsLastChanged)) {
                     this.compileCommandsFileWatcherFallbackTime.set(compileCommandsFile, new Date());
                     this.onCompileCommandsChanged(compileCommandsFile);
                     this.compileCommandsFile = vscode.Uri.file(compileCommandsFile); // File created.