fix(snapshot): improve skipWriting check

Author: antfu

packages/snapshot/src/port/utils.ts

@@ -152,7 +152,7 @@ export async function saveSnapshotFile(
 
   const content = `${environment.getHeader()}\n\n${snapshots.join('\n\n')}\n`
   const oldContent = await environment.readSnapshotFile(snapshotPath)
-  const skipWriting = oldContent && oldContent === content
+  const skipWriting = oldContent != null && oldContent === content
 
   if (skipWriting)
     return
@@ -170,7 +170,7 @@ export async function saveSnapshotFileRaw(
   snapshotPath: string,
 ) {
   const oldContent = await environment.readSnapshotFile(snapshotPath)
-  const skipWriting = oldContent && oldContent === content
+  const skipWriting = oldContent != null && oldContent === content
 
   if (skipWriting)
     return