fix: ignore empty stash

Ignore "No stash entries found." when stashing
is enabled but no files were actually stashed.

Resolves: #55

src/perform-backmerge.ts

@@ -130,7 +130,13 @@ export async function performBackmerge(git: Git, pluginConfig: Partial<Config>,
 
     if (options.restoreWorkspace) {
         context.logger.log('Restoring stashed files to Git workspace.');
-        await git.unstash();
+        try {
+            await git.unstash();
+        } catch (error) {
+            if (!(error instanceof Error) || !(error.message === 'No stash entries found.')) {
+                throw error;
+            }
+        }
     }
 }