Do not close file from deferred function

We were not propagating it correctly and if we were, we would not be
correctly unmapping the file on error. This makes the flow control
easier to follow.

Closes #68

Author: oschwald

reader_other.go

@@ -15,37 +15,37 @@ import (
 func Open(file string) (*Reader, error) {
 	mapFile, err := os.Open(file)
 	if err != nil {
+		_ = mapFile.Close()
 		return nil, err
 	}
-	defer func() {
-		if rerr := mapFile.Close(); rerr != nil {
-			err = rerr
-		}
-	}()
 
 	stats, err := mapFile.Stat()
 	if err != nil {
+		_ = mapFile.Close()
 		return nil, err
 	}
 
 	fileSize := int(stats.Size())
 	mmap, err := mmap(int(mapFile.Fd()), fileSize)
 	if err != nil {
+		_ = mapFile.Close()
+		return nil, err
+	}
+
+	if err := mapFile.Close(); err != nil {
+		_ = munmap(mmap)
 		return nil, err
 	}
 
 	reader, err := FromBytes(mmap)
 	if err != nil {
-		if err2 := munmap(mmap); err2 != nil {
-			// failing to unmap the file is probably the more severe error
-			return nil, err2
-		}
+		_ = munmap(mmap)
 		return nil, err
 	}
 
 	reader.hasMappedFile = true
 	runtime.SetFinalizer(reader, (*Reader).Close)
-	return reader, err
+	return reader, nil
 }
 
 // Close unmaps the database file from virtual memory and returns the