fix: clear previous error when installing extension

Title says it all, clear the previous error. Matches code already in the other extension path.

Fixes #2463.

Signed-off-by: Tim deBoer <git@tdeboer.ca>

packages/renderer/src/lib/docker-extension/PreferencesPageDockerExtensions.svelte

@@ -14,6 +14,7 @@ let logs: string[] = [];
 let logElement;
 
 async function installDDExtensionFromImage() {
+  errorInstall = '';
   logs.length = 0;
   installInProgress = true;