Return early if Python version check fails (#517)

## Summary

This is a follow-up from #516 and adopted from
microsoft/vscode-python-tools-extension-template@723f297.

## Test Plan

Same test plan as #516 but validate that the script failure doesn't
occur now that we exit early.

src/extension.ts

@@ -87,22 +87,21 @@ export async function activate(context: vscode.ExtensionContext): Promise<void>
     restartInProgress = true;
 
     const interpreter = getInterpreterFromSetting(serverId);
-    if (
-      interpreter !== undefined &&
-      interpreter.length > 0 &&
-      checkVersion(await resolveInterpreter(interpreter))
-    ) {
-      traceVerbose(
-        `Using interpreter from ${serverInfo.module}.interpreter: ${interpreter.join(" ")}`,
-      );
-      lsClient = await restartServer(serverId, serverName, outputChannel, lsClient);
+    if (interpreter !== undefined && interpreter.length > 0) {
+      if (checkVersion(await resolveInterpreter(interpreter))) {
+        traceVerbose(
+          `Using interpreter from ${serverInfo.module}.interpreter: ${interpreter.join(" ")}`,
+        );
+        lsClient = await restartServer(serverId, serverName, outputChannel, lsClient);
 
-      restartInProgress = false;
-      if (restartQueued) {
-        restartQueued = false;
-        await runServer();
+        restartInProgress = false;
+        if (restartQueued) {
+          restartQueued = false;
+          await runServer();
+        }
       }
 
+      restartInProgress = false;
       return;
     }