src/goInstallTools: show error if go.languageserver.restart fails

Instead of throwing errors and failing to resolve promise.

Fixes #2356

Change-Id: Ie1bb270217ab12f95e640ccde2d80bfd0eb13292
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/418354
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Jamal Carvalho <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>

Author: hyangah

src/goInstallTools.ts

@@ -191,7 +191,11 @@ export async function installTools(
 			failures.push({ tool, reason: failed });
 		} else if (tool.name === 'gopls') {
 			// Restart the language server if a new binary has been installed.
-			vscode.commands.executeCommand('go.languageserver.restart', RestartReason.INSTALLATION);
+			try {
+				vscode.commands.executeCommand('go.languageserver.restart', RestartReason.INSTALLATION);
+			} catch (e) {
+				vscode.window.showErrorMessage(`Failed to start language server: ${e}`);
+			}
 		}
 	}