refactor: GIF 单独归类、跨文件系统复制回退与异常处理优化

core/bmp.go

@@ -47,8 +47,7 @@ func ReadBmpImage(filePath string) (error, int32, int32) {
 
 	// Check if it's a valid BMP file by verifying the file type.
 	if string(fileHeader.FileType[:]) != "BM" {
-		fmt.Printf("=== Not a valid BMP file: %v\n", err)
-		return err, 0, 0
+		return fmt.Errorf("not a valid BMP file: file type is %q, expected \"BM\"", string(fileHeader.FileType[:])), 0, 0
 	}
 
 	// Read the info header.